[web] Do not wipe the PlatformViewManager when disposing of a view. (flutter#49991)

When a view gets disposed of, its rasterizer completely clears up the singleton `PlatformViewManager`. Particularly, it removes all registered platform view factories.

This is wrong because the remaining PlatformViews on the page cannot be re-rendered, and the default Platform View factories (used by `pointer_interceptor`, for example), disappear.

This PR attempts to preserve the `dispose` logic of the canvaskit rasterizer, without using the `debugClear` method of the `PlatformViewManager` (which is supposedly test-only).

## Issues

* Fixes flutter#142094

## Tests

* Added unit-test
* Deployed demo app: https://dit-maps-tests.web.app

[C++, Objective-C, Java style guides]: https://github.com/flutter/engine/blob/main/CONTRIBUTING.md#style

Author: ditman

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

@@ -410,8 +410,7 @@ class HtmlViewEmbedder {
       // are going to be added back. Moving rather than removing and re-adding
       // the view helps it maintain state.
       disposeViews(diffResult.viewsToRemove
-          .where((int view) => !diffResult.viewsToAdd.contains(view))
-          .toSet());
+          .where((int view) => !diffResult.viewsToAdd.contains(view)));
       _activeCompositionOrder.addAll(_compositionOrder);
       unusedViews.removeAll(_compositionOrder);
 
@@ -510,7 +509,7 @@ class HtmlViewEmbedder {
     );
   }
 
-  void disposeViews(Set<int> viewsToDispose) {
+  void disposeViews(Iterable<int> viewsToDispose) {
     for (final int viewId in viewsToDispose) {
       // Remove viewId from the _viewClipChains Map, and then from the DOM.
       final ViewClipChain? clipChain = _viewClipChains.remove(viewId);
@@ -659,8 +658,7 @@ class HtmlViewEmbedder {
 
   /// Disposes the state of this view embedder.
   void dispose() {
-    final Set<int> allViews = PlatformViewManager.instance.debugClear();
-    disposeViews(allViews);
+    disposeViews(_viewClipChains.keys);
     _context = EmbedderFrameContext();
     _currentCompositionParams.clear();
     debugCleanupSvgClipPaths();

lib/web_ui/lib/src/engine/platform_views/content_manager.dart

@@ -213,16 +213,12 @@ class PlatformViewManager {
   bool isVisible(int viewId) => !isInvisible(viewId);
 
   /// Clears the state. Used in tests.
-  ///
-  /// Returns the set of know view ids, so they can be cleaned up.
-  Set<int> debugClear() {
-    final Set<int> result = _contents.keys.toSet();
-    result.forEach(clearPlatformView);
+  void debugClear() {
+    _contents.keys.toList().forEach(clearPlatformView);
     _factories.clear();
     _contents.clear();
     _invisibleViews.clear();
     _viewIdToType.clear();
-    return result;
   }
 }
 

lib/web_ui/test/canvaskit/multi_view_test.dart

@@ -6,6 +6,7 @@ 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:ui/ui_web/src/ui_web.dart' as ui_web;
 
 import '../common/matchers.dart';
 import 'common.dart';
@@ -68,5 +69,28 @@ void testMain() {
         isNull,
       );
     });
+
+    // Issue https://github.com/flutter/flutter/issues/142094
+    test('does not reset platform view factories when disposing a view', () async {
+      expect(PlatformViewManager.instance.knowsViewType('self-test'), isFalse);
+
+      final EngineFlutterView view = EngineFlutterView(
+          EnginePlatformDispatcher.instance, createDomElement('multi-view'));
+      EnginePlatformDispatcher.instance.viewManager.registerView(view);
+      expect(
+        CanvasKitRenderer.instance.debugGetRasterizerForView(view),
+        isNotNull,
+      );
+
+      EnginePlatformDispatcher.instance.viewManager
+          .disposeAndUnregisterView(view.viewId);
+      expect(
+        CanvasKitRenderer.instance.debugGetRasterizerForView(view),
+        isNull,
+      );
+
+      expect(PlatformViewManager.instance.knowsViewType(ui_web.PlatformViewRegistry.defaultVisibleViewType), isTrue);
+      expect(PlatformViewManager.instance.knowsViewType(ui_web.PlatformViewRegistry.defaultInvisibleViewType), isTrue);
+    });
   });
 }