Do not use try/catch for injectPlatformView flow.

PR comments.

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

@@ -64,15 +64,18 @@ class PlatformViewManager {
     return _contents.containsKey(viewId);
   }
 
-  /// Returns the cached contents of [viewId], to inject them into the DOM.
+  /// Returns the cached contents of [viewId], to be injected into the DOM.
   ///
   /// This is only used by the active `Renderer` object when a platform view needs
   /// to be injected in the DOM, through `FlutterView.DomManager.injectPlatformView`.
   ///
+  /// This may return null, if [renderContent] was not called before this. The
+  /// framework seems to allow/need this for some tests, so it is allowed here
+  /// as well.
+  ///
   /// App programmers should not access this directly, and instead use [getViewById].
-  DomElement getSlottedContent(int viewId) {
-    assert(knowsViewId(viewId), 'No platform view has been rendered with id: $viewId');
-    return _contents[viewId]!;
+  DomElement? getSlottedContent(int viewId) {
+    return _contents[viewId];
   }
 
   /// Returns the HTML element created by a registered factory for [viewId].

lib/web_ui/lib/src/engine/view_embedder/dom_manager.dart

@@ -220,17 +220,16 @@ class DomManager {
   void injectPlatformView(int platformViewId) {
     // For now, we don't need anything fancier. If needed, this can be converted
     // to a PlatformViewStrategy class for each web-renderer backend?
-    try {
-      final DomElement pv = PlatformViewManager.instance.getSlottedContent(platformViewId);
-      // If pv is already a descendant of platformViewsHost -> noop
-      if (pv.parent == platformViewsHost) {
-        return;
-      }
-      platformViewsHost.append(pv);
-    } catch (e) {
-      // Do not fail, many tests expect this to not crash!
-      domWindow.console.warn(e);
+    final DomElement? pv = PlatformViewManager.instance.getSlottedContent(platformViewId);
+    if (pv == null) {
+      domWindow.console.debug('Failed to inject Platform View Id: $platformViewId. Call render first!');
+      return;
     }
+    // If pv is already a descendant of platformViewsHost -> noop
+    if (pv.parent == platformViewsHost) {
+      return;
+    }
+    platformViewsHost.append(pv);
   }
 }
 

lib/web_ui/test/engine/platform_dispatcher/platform_dispatcher_test.dart

@@ -240,15 +240,17 @@ void testMain() {
       expect(view2.isDisposed, isFalse);
 
       bool onMetricsChangedCalled = false;
-      dispatcher.onMetricsChanged = () { 
+      dispatcher.onMetricsChanged = () {
         onMetricsChangedCalled = true;
       };
 
       expect(onMetricsChangedCalled, isFalse);
 
       dispatcher.viewManager.disposeAndUnregisterView(view2.viewId);
 
-      expect(onMetricsChangedCalled, isTrue);
+      expect(onMetricsChangedCalled, isTrue, reason: 'onMetricsChanged should have been called.');
+
+      dispatcher.dispose();
     });
   });
 }