Fix issue from merge conflict.

lib/web_ui/test/ui/frame_timings_test.dart

@@ -6,6 +6,7 @@ import 'dart:async';
 
 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 '../common/test_initialization.dart';
@@ -20,30 +21,31 @@ void testMain() {
   });
 
   test('collects frame timings', () async {
+    final EnginePlatformDispatcher dispatcher = ui.PlatformDispatcher.instance as EnginePlatformDispatcher;
     List<ui.FrameTiming>? timings;
-    ui.PlatformDispatcher.instance.onReportTimings = (List<ui.FrameTiming> data) {
+    dispatcher.onReportTimings = (List<ui.FrameTiming> data) {
       timings = data;
     };
     Completer<void> frameDone = Completer<void>();
-    ui.PlatformDispatcher.instance.onDrawFrame = () {
+    dispatcher.onDrawFrame = () {
       final ui.SceneBuilder sceneBuilder = ui.SceneBuilder();
       sceneBuilder
         ..pushOffset(0, 0)
         ..pop();
-      ui.PlatformDispatcher.instance.render(sceneBuilder.build()).then((_) {
+      dispatcher.render(sceneBuilder.build()).then((_) {
         frameDone.complete();
       });
     };
 
     // Frame 1.
-    ui.PlatformDispatcher.instance.scheduleFrame();
+    dispatcher.scheduleFrame();
     await frameDone.future;
     expect(timings, isNull, reason: "100 ms hasn't passed yet");
     await Future<void>.delayed(const Duration(milliseconds: 150));
 
     // Frame 2.
     frameDone = Completer<void>();
-    ui.PlatformDispatcher.instance.scheduleFrame();
+    dispatcher.scheduleFrame();
     await frameDone.future;
     expect(timings, hasLength(2), reason: '100 ms passed. 2 frames pumped.');
     for (final ui.FrameTiming timing in timings!) {