re-enable pointer events inside platform views (#22874)

lib/web_ui/lib/src/engine/canvaskit/embedded_views.dart

@@ -168,6 +168,10 @@ class HtmlViewEmbedder {
     platformView.style.height = '${params.size.height}px';
     platformView.style.position = 'absolute';
 
+    // <flt-scene-host> disables pointer events. Reenable them here because the
+    // underlying platform view would want to handle the pointer events.
+    platformView.style.pointerEvents = 'auto';
+
     final int currentClippingCount = _countClips(params.mutators);
     final int? previousClippingCount = _clipCount[viewId];
     if (currentClippingCount != previousClippingCount) {

lib/web_ui/test/canvaskit/embedded_views_test.dart

@@ -0,0 +1,64 @@
+// 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:async';
+import 'dart:html' as html;
+
+import 'package:ui/src/engine.dart';
+import 'package:ui/ui.dart' as ui;
+
+import 'package:test/bootstrap/browser.dart';
+import 'package:test/test.dart';
+
+import 'common.dart';
+
+const MethodCodec codec = StandardMethodCodec();
+final EngineSingletonFlutterWindow window = EngineSingletonFlutterWindow(0, EnginePlatformDispatcher.instance);
+
+void main() {
+  internalBootstrapBrowserTest(() => testMain);
+}
+
+void testMain() {
+  group('HtmlViewEmbedder', () {
+    setUpCanvasKitTest();
+
+    test('embeds interactive platform views', () async {
+      ui.platformViewRegistry.registerViewFactory(
+        'test-platform-view',
+        (viewId) => html.DivElement()..id = 'view-0',
+      );
+      await _createPlatformView(0, 'test-platform-view');
+
+      final EnginePlatformDispatcher dispatcher = ui.window.platformDispatcher as EnginePlatformDispatcher;
+      final LayerSceneBuilder sb = LayerSceneBuilder();
+      sb.pushOffset(0, 0);
+      sb.addPlatformView(0, width: 10, height: 10);
+      dispatcher.rasterizer!.draw(sb.build().layerTree);
+      expect(
+        domRenderer.sceneElement!.querySelectorAll('#view-0').single.style.pointerEvents,
+        'auto',
+      );
+    });
+    // TODO: https://github.com/flutter/flutter/issues/60040
+  }, skip: isIosSafari);
+}
+
+// Sends a platform message to create a Platform View with the given id and viewType.
+Future<void> _createPlatformView(int id, String viewType) {
+  final completer = Completer<void>();
+  window.sendPlatformMessage(
+    'flutter/platform_views',
+    codec.encodeMethodCall(MethodCall(
+      'create',
+      <String, dynamic>{
+        'id': id,
+        'viewType': viewType,
+      },
+    )),
+    (dynamic _) => completer.complete(),
+  );
+  return completer.future;
+}