Stop using PlatformViewManager from ck HtmlViewEmbedder.

The HtmlViewEmbedder has enough information to dispose all the views it
knows of (the keys of _viewClipChains), so there's no need to call the
PlatformViewManager to ask for ALL the views in the app.

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);
@@ -659,7 +658,7 @@ class HtmlViewEmbedder {
 
   /// Disposes the state of this view embedder.
   void dispose() {
-    final Set<int> allViews = PlatformViewManager.instance.getKnownPlatformViewIds();
+    final Iterable<int> allViews = _viewClipChains.keys;
     disposeViews(allViews);
     _context = EmbedderFrameContext();
     _currentCompositionParams.clear();

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

@@ -212,18 +212,13 @@ class PlatformViewManager {
   /// component.
   bool isVisible(int viewId) => !isInvisible(viewId);
 
-  /// Returns the set of know view ids, so they can be cleaned up.
-  Set<int> getKnownPlatformViewIds() => _contents.keys.toSet();
-
   /// Clears the state. Used in tests.
-  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;
   }
 }