[web] Provide convenient default factories for platform views

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

@@ -25,6 +25,19 @@ import 'slots.dart';
 /// This class keeps a registry of `factories`, `contents` so the framework can
 /// CRUD Platform Views as needed, regardless of the rendering backend.
 class PlatformViewManager {
+  PlatformViewManager() {
+    // Register some default factories.
+    registerFactory(
+      ui_web.PlatformViewRegistry.defaultVisibleViewType,
+      _defaultFactory,
+    );
+    registerFactory(
+      ui_web.PlatformViewRegistry.defaultInvisibleViewType,
+      _defaultFactory,
+      isVisible: false,
+    );
+  }
+
   // The factory functions, indexed by the viewType
   final Map<String, Function> _factories = <String, Function>{};
 
@@ -223,3 +236,12 @@ class PlatformViewManager {
     return result;
   }
 }
+
+DomElement _defaultFactory(
+  int viewId, {
+  Object? params,
+}) {
+  params!;
+  params as Map<Object?, Object?>;
+  return domDocument.createElement(params.readString('tagName'));
+}

lib/web_ui/lib/ui_web/src/ui_web/platform_view_registry.dart

@@ -19,6 +19,20 @@ final PlatformViewRegistry platformViewRegistry = PlatformViewRegistry();
 
 /// A registry for factories that create platform views.
 class PlatformViewRegistry {
+  /// The view type of the built-in factory that creates visible platform view
+  /// DOM elements.
+  ///
+  /// There's no need to register this view type with [PlatformViewRegistry]
+  /// because it is registered by default.
+  static const String defaultVisibleViewType = '_default_document_create_element_visible';
+
+  /// The view type of the built-in factory that creates invisible platform view
+  /// DOM elements.
+  ///
+  /// There's no need to register this view type with [PlatformViewRegistry]
+  /// because it is registered by default.
+  static const String defaultInvisibleViewType = '_default_document_create_element_invisible';
+
   /// Register [viewType] as being created by the given [viewFactory].
   ///
   /// [viewFactory] can be any function that takes an integer and optional

lib/web_ui/test/engine/platform_views/content_manager_test.dart

@@ -5,8 +5,7 @@
 import 'package:test/bootstrap/browser.dart';
 import 'package:test/test.dart';
 import 'package:ui/src/engine.dart';
-
-import '../../common/matchers.dart';
+import 'package:ui/ui_web/src/ui_web.dart' as ui_web;
 
 void main() {
   internalBootstrapBrowserTest(() => testMain);
@@ -97,13 +96,14 @@ void testMain() {
       });
 
       test('refuse to render views for unregistered factories', () async {
-        try {
-          contentManager.renderContent(unregisteredViewType, viewId, null);
-          fail('renderContent should have thrown an Assertion error!');
-        } catch (e) {
-          expect(e, isAssertionError);
-          expect((e as AssertionError).message, contains(unregisteredViewType));
-        }
+        expect(
+          () => contentManager.renderContent(unregisteredViewType, viewId, null),
+          throwsA(const TypeMatcher<AssertionError>().having(
+            (AssertionError error) => error.message,
+            'assertion message',
+            contains(unregisteredViewType),
+          )),
+        );
       });
 
       test('rendered markup contains required attributes', () async {
@@ -203,5 +203,43 @@ void testMain() {
         }, throwsA(isA<AssertionError>()));
       });
     });
+
+    test('default factories', () {
+      final DomElement content0 = contentManager.renderContent(
+        ui_web.PlatformViewRegistry.defaultVisibleViewType,
+        viewId,
+        <dynamic, dynamic>{'tagName': 'table'},
+      );
+      expect(
+        contentManager.getViewById(viewId),
+        content0.querySelector('table'),
+      );
+      expect(contentManager.isVisible(viewId), isTrue);
+      expect(contentManager.isInvisible(viewId), isFalse);
+
+      final DomElement content1 = contentManager.renderContent(
+        ui_web.PlatformViewRegistry.defaultInvisibleViewType,
+        viewId + 1,
+        <dynamic, dynamic>{'tagName': 'script'},
+      );
+      expect(
+        contentManager.getViewById(viewId + 1),
+        content1.querySelector('script'),
+      );
+      expect(contentManager.isVisible(viewId + 1), isFalse);
+      expect(contentManager.isInvisible(viewId + 1), isTrue);
+
+      final DomElement content2 = contentManager.renderContent(
+        ui_web.PlatformViewRegistry.defaultVisibleViewType,
+        viewId + 2,
+        <dynamic, dynamic>{'tagName': 'p'},
+      );
+      expect(
+        contentManager.getViewById(viewId + 2),
+        content2.querySelector('p'),
+      );
+      expect(contentManager.isVisible(viewId + 2), isTrue);
+      expect(contentManager.isInvisible(viewId + 2), isFalse);
+    });
   });
 }