Pass angles for SweepGradient in degrees, not radians (flutter/engine#21677)

engine/src/flutter/lib/web_ui/lib/src/engine/canvaskit/shader.dart

@@ -35,6 +35,7 @@ class CkGradientSweep extends CkShader implements ui.Gradient {
 
   @override
   SkShader createDefault() {
+    const double toDegrees = 180.0 / math.pi;
     return canvasKit.Shader.MakeSweepGradient(
       center.dx,
       center.dy,
@@ -43,8 +44,8 @@ class CkGradientSweep extends CkShader implements ui.Gradient {
       toSkTileMode(tileMode),
       matrix4 != null ? toSkMatrixFromFloat32(matrix4!) : null,
       0,
-      startAngle,
-      endAngle,
+      toDegrees * startAngle,
+      toDegrees * endAngle,
     );
   }
 

engine/src/flutter/lib/web_ui/test/canvaskit/sweep_gradient_golden_test.dart

@@ -0,0 +1,75 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// @dart = 2.12
+import 'dart:math' as math;
+
+import 'package:test/bootstrap/browser.dart';
+import 'package:test/test.dart';
+import 'package:ui/src/engine.dart';
+import 'package:ui/ui.dart' as ui;
+
+import 'package:web_engine_tester/golden_tester.dart';
+
+import 'common.dart';
+
+void main() {
+  internalBootstrapBrowserTest(() => testMain);
+}
+
+const ui.Rect region = const ui.Rect.fromLTRB(0, 0, 500, 250);
+
+Future<void> matchPictureGolden(String goldenFile, CkPicture picture,
+    {bool write = false}) async {
+  final EnginePlatformDispatcher dispatcher =
+      ui.window.platformDispatcher as EnginePlatformDispatcher;
+  final LayerSceneBuilder sb = LayerSceneBuilder();
+  sb.pushOffset(0, 0);
+  sb.addPicture(ui.Offset.zero, picture);
+  dispatcher.rasterizer!.draw(sb.build().layerTree);
+  await matchGoldenFile(goldenFile, region: region, write: write);
+}
+
+void testMain() {
+  group('SweepGradient', () {
+    setUpCanvasKitTest();
+
+    test('is correctly rendered', () async {
+      final CkPictureRecorder recorder = CkPictureRecorder();
+      final CkCanvas canvas = recorder.beginRecording(region);
+
+      final CkGradientSweep gradient = CkGradientSweep(
+          ui.Offset(250, 125),
+          <ui.Color>[
+            ui.Color(0xFF4285F4),
+            ui.Color(0xFF34A853),
+            ui.Color(0xFFFBBC05),
+            ui.Color(0xFFEA4335),
+            ui.Color(0xFF4285F4),
+          ],
+          <double>[
+            0.0,
+            0.25,
+            0.5,
+            0.75,
+            1.0,
+          ],
+          ui.TileMode.clamp,
+          -(math.pi / 2),
+          math.pi * 2 - (math.pi / 2),
+          null);
+
+      final CkPaint paint = CkPaint()..shader = gradient;
+
+      canvas.drawRect(region, paint);
+
+      await matchPictureGolden(
+        'canvaskit_sweep_gradient.png',
+        recorder.endRecording(),
+      );
+    });
+    // TODO: https://github.com/flutter/flutter/issues/60040
+    // TODO: https://github.com/flutter/flutter/issues/71520
+  }, skip: isIosSafari || isFirefox);
+}