diff --git a/dev/devicelab/bin/tasks/analyzer_benchmark.dart b/dev/devicelab/bin/tasks/analyzer_benchmark.dart
index c8d092a049b..3ded9ba7fcf 100644
--- a/dev/devicelab/bin/tasks/analyzer_benchmark.dart
+++ b/dev/devicelab/bin/tasks/analyzer_benchmark.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/analysis.dart';
 
diff --git a/dev/devicelab/bin/tasks/android_defines_test.dart b/dev/devicelab/bin/tasks/android_defines_test.dart
index 2f31c1133f0..9774212a1de 100644
--- a/dev/devicelab/bin/tasks/android_defines_test.dart
+++ b/dev/devicelab/bin/tasks/android_defines_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/android_engine_dependency_proxy_test.dart b/dev/devicelab/bin/tasks/android_engine_dependency_proxy_test.dart
index 314854d0d0e..69a663f3900 100644
--- a/dev/devicelab/bin/tasks/android_engine_dependency_proxy_test.dart
+++ b/dev/devicelab/bin/tasks/android_engine_dependency_proxy_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/apk_utils.dart';
@@ -18,7 +20,7 @@ Future<void> main() async {
   await task(() async {
     section('Find Java');
 
-    final String? javaHome = await findJavaHome();
+    final String javaHome = await findJavaHome();
     if (javaHome == null)
       return TaskResult.failure('Could not find Java');
     print('\nUsing JAVA_HOME=$javaHome');
diff --git a/dev/devicelab/bin/tasks/android_obfuscate_test.dart b/dev/devicelab/bin/tasks/android_obfuscate_test.dart
index 6676a0d61fc..7e4429e413c 100644
--- a/dev/devicelab/bin/tasks/android_obfuscate_test.dart
+++ b/dev/devicelab/bin/tasks/android_obfuscate_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/apk_utils.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/task_result.dart';
diff --git a/dev/devicelab/bin/tasks/android_semantics_integration_test.dart b/dev/devicelab/bin/tasks/android_semantics_integration_test.dart
index 415fad2eca9..d2ce3e47f7d 100644
--- a/dev/devicelab/bin/tasks/android_semantics_integration_test.dart
+++ b/dev/devicelab/bin/tasks/android_semantics_integration_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/android_stack_size_test.dart b/dev/devicelab/bin/tasks/android_stack_size_test.dart
index 80341ffa246..546aef2d79c 100644
--- a/dev/devicelab/bin/tasks/android_stack_size_test.dart
+++ b/dev/devicelab/bin/tasks/android_stack_size_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/android_view_scroll_perf__timeline_summary.dart b/dev/devicelab/bin/tasks/android_view_scroll_perf__timeline_summary.dart
index 1112ba20e84..22e2df478fb 100644
--- a/dev/devicelab/bin/tasks/android_view_scroll_perf__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/android_view_scroll_perf__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/animated_image_gc_perf.dart b/dev/devicelab/bin/tasks/animated_image_gc_perf.dart
index b5fe9f8e0ce..65f456ee304 100644
--- a/dev/devicelab/bin/tasks/animated_image_gc_perf.dart
+++ b/dev/devicelab/bin/tasks/animated_image_gc_perf.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
diff --git a/dev/devicelab/bin/tasks/animated_placeholder_perf__e2e_summary.dart b/dev/devicelab/bin/tasks/animated_placeholder_perf__e2e_summary.dart
index e8986d8930f..ec033b3bff6 100644
--- a/dev/devicelab/bin/tasks/animated_placeholder_perf__e2e_summary.dart
+++ b/dev/devicelab/bin/tasks/animated_placeholder_perf__e2e_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:async';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/animation_with_microtasks_perf_ios__timeline_summary.dart b/dev/devicelab/bin/tasks/animation_with_microtasks_perf_ios__timeline_summary.dart
index 8ecc0bacff6..c84450eda72 100644
--- a/dev/devicelab/bin/tasks/animation_with_microtasks_perf_ios__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/animation_with_microtasks_perf_ios__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/backdrop_filter_perf__e2e_summary.dart b/dev/devicelab/bin/tasks/backdrop_filter_perf__e2e_summary.dart
index 141e2c23b68..49b216f5154 100644
--- a/dev/devicelab/bin/tasks/backdrop_filter_perf__e2e_summary.dart
+++ b/dev/devicelab/bin/tasks/backdrop_filter_perf__e2e_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:async';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/backdrop_filter_perf__timeline_summary.dart b/dev/devicelab/bin/tasks/backdrop_filter_perf__timeline_summary.dart
index 1b59f9da0e9..db1ec8f7b91 100644
--- a/dev/devicelab/bin/tasks/backdrop_filter_perf__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/backdrop_filter_perf__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/backdrop_filter_perf_ios__timeline_summary.dart b/dev/devicelab/bin/tasks/backdrop_filter_perf_ios__timeline_summary.dart
index 6a63a8b9165..354d3694ea2 100644
--- a/dev/devicelab/bin/tasks/backdrop_filter_perf_ios__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/backdrop_filter_perf_ios__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/basic_material_app_android__compile.dart b/dev/devicelab/bin/tasks/basic_material_app_android__compile.dart
index cf903c03f93..6b93fad7d7a 100644
--- a/dev/devicelab/bin/tasks/basic_material_app_android__compile.dart
+++ b/dev/devicelab/bin/tasks/basic_material_app_android__compile.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/basic_material_app_ios__compile.dart b/dev/devicelab/bin/tasks/basic_material_app_ios__compile.dart
index cc6f0f7c2ca..e503d0a5edf 100644
--- a/dev/devicelab/bin/tasks/basic_material_app_ios__compile.dart
+++ b/dev/devicelab/bin/tasks/basic_material_app_ios__compile.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/basic_material_app_win__compile.dart b/dev/devicelab/bin/tasks/basic_material_app_win__compile.dart
index cf903c03f93..6b93fad7d7a 100644
--- a/dev/devicelab/bin/tasks/basic_material_app_win__compile.dart
+++ b/dev/devicelab/bin/tasks/basic_material_app_win__compile.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/build_aar_module_test.dart b/dev/devicelab/bin/tasks/build_aar_module_test.dart
index 3a78801ad6b..5c03498aff1 100644
--- a/dev/devicelab/bin/tasks/build_aar_module_test.dart
+++ b/dev/devicelab/bin/tasks/build_aar_module_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/apk_utils.dart';
@@ -22,7 +24,7 @@ Future<void> main() async {
 
     section('Find Java');
 
-    final String? javaHome = await findJavaHome();
+    final String javaHome = await findJavaHome();
     if (javaHome == null)
       return TaskResult.failure('Could not find Java');
     print('\nUsing JAVA_HOME=$javaHome');
diff --git a/dev/devicelab/bin/tasks/build_aar_plugin_test.dart b/dev/devicelab/bin/tasks/build_aar_plugin_test.dart
index e0df9586d1b..6f666d26602 100644
--- a/dev/devicelab/bin/tasks/build_aar_plugin_test.dart
+++ b/dev/devicelab/bin/tasks/build_aar_plugin_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/framework.dart';
@@ -18,7 +20,7 @@ Future<void> main() async {
 
     section('Find Java');
 
-    final String? javaHome = await findJavaHome();
+    final String javaHome = await findJavaHome();
     if (javaHome == null)
       return TaskResult.failure('Could not find Java');
     print('\nUsing JAVA_HOME=$javaHome');
diff --git a/dev/devicelab/bin/tasks/build_ios_framework_module_test.dart b/dev/devicelab/bin/tasks/build_ios_framework_module_test.dart
index 63b59ab28c4..05fd14d5c0c 100644
--- a/dev/devicelab/bin/tasks/build_ios_framework_module_test.dart
+++ b/dev/devicelab/bin/tasks/build_ios_framework_module_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/framework.dart';
diff --git a/dev/devicelab/bin/tasks/build_mode_test.dart b/dev/devicelab/bin/tasks/build_mode_test.dart
index e73625a9a9d..23f739bab54 100644
--- a/dev/devicelab/bin/tasks/build_mode_test.dart
+++ b/dev/devicelab/bin/tasks/build_mode_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:async';
 import 'dart:convert';
 import 'dart:io';
@@ -23,7 +25,7 @@ Future<String> runFlutterAndQuit(List<String> args, Device device) async {
   );
   final List<String> stdout = <String>[];
   final List<String> stderr = <String>[];
-  int? runExitCode;
+  int runExitCode;
   run.stdout.transform<String>(utf8.decoder).transform<String>(const LineSplitter()).listen(
     (String line) {
       print('run:stdout: $line');
diff --git a/dev/devicelab/bin/tasks/channels_integration_test.dart b/dev/devicelab/bin/tasks/channels_integration_test.dart
index c1cb7b8e8b2..e842be1b6c9 100644
--- a/dev/devicelab/bin/tasks/channels_integration_test.dart
+++ b/dev/devicelab/bin/tasks/channels_integration_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/channels_integration_test_ios.dart b/dev/devicelab/bin/tasks/channels_integration_test_ios.dart
index 41f042291cb..9445f9b1bb1 100644
--- a/dev/devicelab/bin/tasks/channels_integration_test_ios.dart
+++ b/dev/devicelab/bin/tasks/channels_integration_test_ios.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/channels_integration_test_win.dart b/dev/devicelab/bin/tasks/channels_integration_test_win.dart
index c1cb7b8e8b2..e842be1b6c9 100644
--- a/dev/devicelab/bin/tasks/channels_integration_test_win.dart
+++ b/dev/devicelab/bin/tasks/channels_integration_test_win.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/codegen_integration_linux.dart b/dev/devicelab/bin/tasks/codegen_integration_linux.dart
index 57eab92aeb5..f7dae49a44d 100644
--- a/dev/devicelab/bin/tasks/codegen_integration_linux.dart
+++ b/dev/devicelab/bin/tasks/codegen_integration_linux.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/codegen_integration_mac.dart b/dev/devicelab/bin/tasks/codegen_integration_mac.dart
index a1d76af3e3f..2501d7b7b79 100644
--- a/dev/devicelab/bin/tasks/codegen_integration_mac.dart
+++ b/dev/devicelab/bin/tasks/codegen_integration_mac.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/codegen_integration_win.dart b/dev/devicelab/bin/tasks/codegen_integration_win.dart
index 57eab92aeb5..f7dae49a44d 100644
--- a/dev/devicelab/bin/tasks/codegen_integration_win.dart
+++ b/dev/devicelab/bin/tasks/codegen_integration_win.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/color_filter_and_fade_perf__e2e_summary.dart b/dev/devicelab/bin/tasks/color_filter_and_fade_perf__e2e_summary.dart
index 5ec07b7c7f8..e63db6ecfee 100644
--- a/dev/devicelab/bin/tasks/color_filter_and_fade_perf__e2e_summary.dart
+++ b/dev/devicelab/bin/tasks/color_filter_and_fade_perf__e2e_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:async';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/color_filter_and_fade_perf__timeline_summary.dart b/dev/devicelab/bin/tasks/color_filter_and_fade_perf__timeline_summary.dart
index 234b43b4568..62439a7eb46 100644
--- a/dev/devicelab/bin/tasks/color_filter_and_fade_perf__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/color_filter_and_fade_perf__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout__start_up.dart b/dev/devicelab/bin/tasks/complex_layout__start_up.dart
index 12c6d9a862d..c05c700cb2c 100644
--- a/dev/devicelab/bin/tasks/complex_layout__start_up.dart
+++ b/dev/devicelab/bin/tasks/complex_layout__start_up.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_android__compile.dart b/dev/devicelab/bin/tasks/complex_layout_android__compile.dart
index 4bc85ca1c27..41ad9847cc2 100644
--- a/dev/devicelab/bin/tasks/complex_layout_android__compile.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_android__compile.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_android__scroll_smoothness.dart b/dev/devicelab/bin/tasks/complex_layout_android__scroll_smoothness.dart
index 7fe5461cc4d..0503f776481 100644
--- a/dev/devicelab/bin/tasks/complex_layout_android__scroll_smoothness.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_android__scroll_smoothness.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:async';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_ios__compile.dart b/dev/devicelab/bin/tasks/complex_layout_ios__compile.dart
index d8600c22cb2..36fd39a2846 100644
--- a/dev/devicelab/bin/tasks/complex_layout_ios__compile.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_ios__compile.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_ios__start_up.dart b/dev/devicelab/bin/tasks/complex_layout_ios__start_up.dart
index 2bb3a269243..4548bffb38d 100644
--- a/dev/devicelab/bin/tasks/complex_layout_ios__start_up.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_ios__start_up.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_scroll_perf__devtools_memory.dart b/dev/devicelab/bin/tasks/complex_layout_scroll_perf__devtools_memory.dart
index de449f3b59f..94f0614f99e 100644
--- a/dev/devicelab/bin/tasks/complex_layout_scroll_perf__devtools_memory.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_scroll_perf__devtools_memory.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_scroll_perf__memory.dart b/dev/devicelab/bin/tasks/complex_layout_scroll_perf__memory.dart
index f3784a3b30e..8b0146fb7bf 100644
--- a/dev/devicelab/bin/tasks/complex_layout_scroll_perf__memory.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_scroll_perf__memory.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_scroll_perf__timeline_summary.dart b/dev/devicelab/bin/tasks/complex_layout_scroll_perf__timeline_summary.dart
index d4f1878846e..95cb14fce0b 100644
--- a/dev/devicelab/bin/tasks/complex_layout_scroll_perf__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_scroll_perf__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_scroll_perf_ios__timeline_summary.dart b/dev/devicelab/bin/tasks/complex_layout_scroll_perf_ios__timeline_summary.dart
index b514d357417..b9a3cd7dd85 100644
--- a/dev/devicelab/bin/tasks/complex_layout_scroll_perf_ios__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_scroll_perf_ios__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_semantics_perf.dart b/dev/devicelab/bin/tasks/complex_layout_semantics_perf.dart
index ab1d4b7c123..0a40d263f97 100644
--- a/dev/devicelab/bin/tasks/complex_layout_semantics_perf.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_semantics_perf.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:io';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/complex_layout_win__compile.dart b/dev/devicelab/bin/tasks/complex_layout_win__compile.dart
index 4bc85ca1c27..41ad9847cc2 100644
--- a/dev/devicelab/bin/tasks/complex_layout_win__compile.dart
+++ b/dev/devicelab/bin/tasks/complex_layout_win__compile.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/cubic_bezier_perf__e2e_summary.dart b/dev/devicelab/bin/tasks/cubic_bezier_perf__e2e_summary.dart
index 437982f508a..4dfb8c5237e 100644
--- a/dev/devicelab/bin/tasks/cubic_bezier_perf__e2e_summary.dart
+++ b/dev/devicelab/bin/tasks/cubic_bezier_perf__e2e_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:async';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/cubic_bezier_perf__timeline_summary.dart b/dev/devicelab/bin/tasks/cubic_bezier_perf__timeline_summary.dart
index 2a1ad712d53..352f559110c 100644
--- a/dev/devicelab/bin/tasks/cubic_bezier_perf__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/cubic_bezier_perf__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/cubic_bezier_perf_sksl_warmup__e2e_summary.dart b/dev/devicelab/bin/tasks/cubic_bezier_perf_sksl_warmup__e2e_summary.dart
index 38d83b1e216..0bad40559a1 100644
--- a/dev/devicelab/bin/tasks/cubic_bezier_perf_sksl_warmup__e2e_summary.dart
+++ b/dev/devicelab/bin/tasks/cubic_bezier_perf_sksl_warmup__e2e_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'dart:async';
 
 import 'package:flutter_devicelab/framework/devices.dart';
diff --git a/dev/devicelab/bin/tasks/cubic_bezier_perf_sksl_warmup__timeline_summary.dart b/dev/devicelab/bin/tasks/cubic_bezier_perf_sksl_warmup__timeline_summary.dart
index 83eb00361c3..ae086b49287 100644
--- a/dev/devicelab/bin/tasks/cubic_bezier_perf_sksl_warmup__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/cubic_bezier_perf_sksl_warmup__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/cull_opacity_perf__e2e_summary.dart b/dev/devicelab/bin/tasks/cull_opacity_perf__e2e_summary.dart
index 593641abac3..2e6adeca8bc 100644
--- a/dev/devicelab/bin/tasks/cull_opacity_perf__e2e_summary.dart
+++ b/dev/devicelab/bin/tasks/cull_opacity_perf__e2e_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/cull_opacity_perf__timeline_summary.dart b/dev/devicelab/bin/tasks/cull_opacity_perf__timeline_summary.dart
index 9840170a09c..b51ded429c7 100644
--- a/dev/devicelab/bin/tasks/cull_opacity_perf__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/cull_opacity_perf__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/dart_plugin_registry_test.dart b/dev/devicelab/bin/tasks/dart_plugin_registry_test.dart
index 1688aadf79a..1ddd1213c4d 100644
--- a/dev/devicelab/bin/tasks/dart_plugin_registry_test.dart
+++ b/dev/devicelab/bin/tasks/dart_plugin_registry_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/dart_plugin_registry_tests.dart';
 
diff --git a/dev/devicelab/bin/tasks/dartdocs.dart b/dev/devicelab/bin/tasks/dartdocs.dart
index 0bb2d2093c9..0a11a2e37b6 100644
--- a/dev/devicelab/bin/tasks/dartdocs.dart
+++ b/dev/devicelab/bin/tasks/dartdocs.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/task_result.dart';
 
diff --git a/dev/devicelab/bin/tasks/devtools_profile_start_test.dart b/dev/devicelab/bin/tasks/devtools_profile_start_test.dart
index 11959b5bc46..5d1f8afe4fd 100644
--- a/dev/devicelab/bin/tasks/devtools_profile_start_test.dart
+++ b/dev/devicelab/bin/tasks/devtools_profile_start_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
diff --git a/dev/devicelab/bin/tasks/drive_perf_debug_warning.dart b/dev/devicelab/bin/tasks/drive_perf_debug_warning.dart
index 0390ad891ec..08be1676240 100644
--- a/dev/devicelab/bin/tasks/drive_perf_debug_warning.dart
+++ b/dev/devicelab/bin/tasks/drive_perf_debug_warning.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/task_result.dart';
diff --git a/dev/devicelab/bin/tasks/embedded_android_views_integration_test.dart b/dev/devicelab/bin/tasks/embedded_android_views_integration_test.dart
index c13bc789f00..8bf3425e8ce 100644
--- a/dev/devicelab/bin/tasks/embedded_android_views_integration_test.dart
+++ b/dev/devicelab/bin/tasks/embedded_android_views_integration_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/external_ui_integration_test.dart b/dev/devicelab/bin/tasks/external_ui_integration_test.dart
index cc0930ea734..793bd5c719b 100644
--- a/dev/devicelab/bin/tasks/external_ui_integration_test.dart
+++ b/dev/devicelab/bin/tasks/external_ui_integration_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/external_ui_integration_test_ios.dart b/dev/devicelab/bin/tasks/external_ui_integration_test_ios.dart
index a573cc1b611..3174d152a6e 100644
--- a/dev/devicelab/bin/tasks/external_ui_integration_test_ios.dart
+++ b/dev/devicelab/bin/tasks/external_ui_integration_test_ios.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/fading_child_animation_perf__timeline_summary.dart b/dev/devicelab/bin/tasks/fading_child_animation_perf__timeline_summary.dart
index dbed0b3c4d5..14ea384c1d0 100644
--- a/dev/devicelab/bin/tasks/fading_child_animation_perf__timeline_summary.dart
+++ b/dev/devicelab/bin/tasks/fading_child_animation_perf__timeline_summary.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/perf_tests.dart';
diff --git a/dev/devicelab/bin/tasks/fast_scroll_heavy_gridview__memory.dart b/dev/devicelab/bin/tasks/fast_scroll_heavy_gridview__memory.dart
index 9c8c38bada9..3d7d393339d 100644
--- a/dev/devicelab/bin/tasks/fast_scroll_heavy_gridview__memory.dart
+++ b/dev/devicelab/bin/tasks/fast_scroll_heavy_gridview__memory.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
@@ -18,7 +20,7 @@ class FastScrollHeavyGridViewMemoryTest extends MemoryTest {
         );
 
   @override
-  AndroidDevice? get device => super.device as AndroidDevice?;
+  AndroidDevice get device => super.device as AndroidDevice;
 
   @override
   int get iterationCount => 5;
@@ -27,11 +29,11 @@ class FastScrollHeavyGridViewMemoryTest extends MemoryTest {
   Future<void> useMemory() async {
     await launchApp();
     await recordStart();
-    await device!.shellExec('input', <String>['swipe', '50 1500 50 50 50']);
+    await device.shellExec('input', <String>['swipe', '50 1500 50 50 50']);
     await Future<void>.delayed(const Duration(milliseconds: 1500));
-    await device!.shellExec('input', <String>['swipe', '50 1500 50 50 50']);
+    await device.shellExec('input', <String>['swipe', '50 1500 50 50 50']);
     await Future<void>.delayed(const Duration(milliseconds: 1500));
-    await device!.shellExec('input', <String>['swipe', '50 1500 50 50 50']);
+    await device.shellExec('input', <String>['swipe', '50 1500 50 50 50']);
     await Future<void>.delayed(const Duration(milliseconds: 1500));
     await recordEnd();
   }
diff --git a/dev/devicelab/bin/tasks/fast_scroll_large_images__memory.dart b/dev/devicelab/bin/tasks/fast_scroll_large_images__memory.dart
index 26b76c2a411..e61adf6c7e2 100644
--- a/dev/devicelab/bin/tasks/fast_scroll_large_images__memory.dart
+++ b/dev/devicelab/bin/tasks/fast_scroll_large_images__memory.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/framework/utils.dart';
@@ -18,7 +20,7 @@ class FastScrollLargeImagesMemoryTest extends MemoryTest {
         );
 
   @override
-  AndroidDevice? get device => super.device as AndroidDevice?;
+  AndroidDevice get device => super.device as AndroidDevice;
 
   @override
   int get iterationCount => 5;
@@ -27,7 +29,7 @@ class FastScrollLargeImagesMemoryTest extends MemoryTest {
   Future<void> useMemory() async {
     await launchApp();
     await recordStart();
-    await device!.shellExec('input', <String>['swipe', '0 1500 0 0 50']);
+    await device.shellExec('input', <String>['swipe', '0 1500 0 0 50']);
     await Future<void>.delayed(const Duration(milliseconds: 15000));
     await recordEnd();
   }
diff --git a/dev/devicelab/bin/tasks/flavors_test.dart b/dev/devicelab/bin/tasks/flavors_test.dart
index b8fbade6610..92e1522b6e3 100644
--- a/dev/devicelab/bin/tasks/flavors_test.dart
+++ b/dev/devicelab/bin/tasks/flavors_test.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/flavors_test_ios.dart b/dev/devicelab/bin/tasks/flavors_test_ios.dart
index 3fa97b2cf7b..c20de247a2a 100644
--- a/dev/devicelab/bin/tasks/flavors_test_ios.dart
+++ b/dev/devicelab/bin/tasks/flavors_test_ios.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';
diff --git a/dev/devicelab/bin/tasks/flavors_test_win.dart b/dev/devicelab/bin/tasks/flavors_test_win.dart
index b8fbade6610..92e1522b6e3 100644
--- a/dev/devicelab/bin/tasks/flavors_test_win.dart
+++ b/dev/devicelab/bin/tasks/flavors_test_win.dart
@@ -2,6 +2,8 @@
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
+// @dart = 2.8
+
 import 'package:flutter_devicelab/framework/devices.dart';
 import 'package:flutter_devicelab/framework/framework.dart';
 import 'package:flutter_devicelab/tasks/integration_tests.dart';