Fix analysis errors

lib/web_ui/test/canvaskit/multi_view_test.dart

@@ -33,13 +33,13 @@ void testMain() {
     });
 
     test('can render into arbitrary views', () async {
-      CanvasKitRenderer.instance.renderScene(scene, implicitView);
+      await CanvasKitRenderer.instance.renderScene(scene, implicitView);
 
       final EngineFlutterView anotherView = EngineFlutterView(
           EnginePlatformDispatcher.instance, createDomElement('another-view'));
       EnginePlatformDispatcher.instance.viewManager.registerView(anotherView);
 
-      CanvasKitRenderer.instance.renderScene(scene, anotherView);
+      await CanvasKitRenderer.instance.renderScene(scene, anotherView);
     });
 
     test('will error if trying to render into an unregistered view', () async {

lib/web_ui/test/canvaskit/render_canvas_test.dart

@@ -21,13 +21,13 @@ void testMain() {
     });
 
     Future<DomImageBitmap> newBitmap(int width, int height) async {
-      return (await createImageBitmap(
+      return createImageBitmap(
           createBlankDomImageData(width, height) as JSAny, (
         x: 0,
         y: 0,
         width: width,
         height: height,
-      )).toDart)! as DomImageBitmap;
+      ));
     }
 
     // Regression test for https://github.com/flutter/flutter/issues/75286

lib/web_ui/test/engine/scene_view_test.dart

@@ -26,10 +26,13 @@ class StubPictureRenderer implements PictureRenderer {
   Future<DomImageBitmap> renderPicture(ScenePicture picture) async {
     renderedPictures.add(picture);
     final ui.Rect cullRect = picture.cullRect;
-    final DomImageBitmap bitmap = (await createImageBitmap(
-      scratchCanvasElement as JSObject,
-      (x: 0, y: 0, width: cullRect.width.toInt(), height: cullRect.height.toInt())
-    ).toDart)! as DomImageBitmap;
+    final DomImageBitmap bitmap =
+        await createImageBitmap(scratchCanvasElement as JSObject, (
+      x: 0,
+      y: 0,
+      width: cullRect.width.toInt(),
+      height: cullRect.height.toInt(),
+    ));
     return bitmap;
   }
 
@@ -83,7 +86,8 @@ void testMain() {
     debugOverrideDevicePixelRatio(null);
   });
 
-  test('SceneView places platform view according to device-pixel ratio', () async {
+  test('SceneView places platform view according to device-pixel ratio',
+      () async {
     debugOverrideDevicePixelRatio(2.0);
 
     final PlatformView platformView = PlatformView(
@@ -113,7 +117,9 @@ void testMain() {
     debugOverrideDevicePixelRatio(null);
   });
 
-  test('SceneView always renders most recent picture and skips intermediate pictures', () async {
+  test(
+      'SceneView always renders most recent picture and skips intermediate pictures',
+      () async {
     final List<StubPicture> pictures = <StubPicture>[];
     final List<Future<void>> renderFutures = <Future<void>>[];
     for (int i = 1; i < 20; i++) {

lib/web_ui/test/ui/image_golden_test.dart

@@ -318,7 +318,7 @@ Future<void> testMain() async {
       image.src = url;
       await completer.future;
 
-      final DomImageBitmap bitmap = (await createImageBitmap(image as JSObject).toDart)! as DomImageBitmap;
+      final DomImageBitmap bitmap = await createImageBitmap(image as JSObject);
 
       expect(bitmap.width.toDartInt, 150);
       expect(bitmap.height.toDartInt, 150);