Respond to Skia platform messages (flutter#24880)

Author: yjbanov

lib/web_ui/lib/src/engine/platform_dispatcher.dart

@@ -333,9 +333,20 @@ class EnginePlatformDispatcher extends ui.PlatformDispatcher {
         final MethodCall decoded = codec.decodeMethodCall(data);
         switch (decoded.method) {
           case 'Skia.setResourceCacheMaxBytes':
-            if (decoded.arguments is int) {
-              rasterizer?.setSkiaResourceCacheMaxBytes(decoded.arguments);
+            if (useCanvasKit) {
+              // If we're in CanvasKit mode, we must also have a rasterizer.
+              assert(rasterizer != null);
+              assert(
+                decoded.arguments is int,
+                'Argument to Skia.setResourceCacheMaxBytes must be an int, but was ${decoded.arguments.runtimeType}',
+              );
+              final int cacheSizeInBytes = decoded.arguments as int;
+              rasterizer!.setSkiaResourceCacheMaxBytes(cacheSizeInBytes);
             }
+
+            // Also respond in HTML mode. Otherwise, apps would have to detect
+            // CanvasKit vs HTML before invoking this method.
+            _replyToPlatformMessage(callback, codec.encodeSuccessEnvelope([true]));
             break;
         }
         return;
@@ -896,9 +907,9 @@ class EnginePlatformDispatcher extends ui.PlatformDispatcher {
   /// messages and responses have to be exchanged asynchronously. We simulate
   /// that by adding a zero-length delay to the reply.
   void _replyToPlatformMessage(
-      ui.PlatformMessageResponseCallback? callback,
-      ByteData? data,
-      ) {
+    ui.PlatformMessageResponseCallback? callback,
+    ByteData? data,
+  ) {
     Future<void>.delayed(Duration.zero).then((_) {
       if (callback != null) {
         callback(data);

lib/web_ui/test/canvaskit/platform_dispatcher_test.dart

@@ -0,0 +1,46 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// @dart = 2.12
+import 'dart:async';
+import 'dart:typed_data';
+
+import 'package:ui/src/engine.dart';
+import 'package:ui/ui.dart' as ui;
+
+import 'package:test/bootstrap/browser.dart';
+import 'package:test/test.dart';
+
+import 'common.dart';
+
+void main() {
+  internalBootstrapBrowserTest(() => testMain);
+}
+
+void testMain() {
+  group('PlatformDispatcher', () {
+    setUpCanvasKitTest();
+
+    test('responds to flutter/skia Skia.setResourceCacheMaxBytes', () async {
+      const MethodCodec codec = JSONMethodCodec();
+      final Completer<ByteData?> completer = Completer<ByteData?>();
+      ui.PlatformDispatcher.instance.sendPlatformMessage(
+        'flutter/skia',
+        codec.encodeMethodCall(MethodCall(
+          'Skia.setResourceCacheMaxBytes',
+          512 * 1000 * 1000,
+        )),
+        completer.complete,
+      );
+
+      final ByteData? response = await completer.future;
+      expect(response, isNotNull);
+      expect(
+        codec.decodeEnvelope(response!),
+        [true],
+      );
+    });
+    // TODO: https://github.com/flutter/flutter/issues/60040
+  }, skip: isIosSafari);
+}

lib/web_ui/test/engine/platform_dispatcher_test.dart

@@ -0,0 +1,41 @@
+// Copyright 2013 The Flutter Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+// @dart = 2.12
+import 'dart:async';
+import 'dart:typed_data';
+
+import 'package:ui/src/engine.dart';
+import 'package:ui/ui.dart' as ui;
+
+import 'package:test/bootstrap/browser.dart';
+import 'package:test/test.dart';
+
+void main() {
+  internalBootstrapBrowserTest(() => testMain);
+}
+
+void testMain() {
+  group('PlatformDispatcher', () {
+    test('responds to flutter/skia Skia.setResourceCacheMaxBytes', () async {
+      const MethodCodec codec = JSONMethodCodec();
+      final Completer<ByteData?> completer = Completer<ByteData?>();
+      ui.PlatformDispatcher.instance.sendPlatformMessage(
+        'flutter/skia',
+        codec.encodeMethodCall(MethodCall(
+          'Skia.setResourceCacheMaxBytes',
+          512 * 1000 * 1000,
+        )),
+        completer.complete,
+      );
+
+      final ByteData? response = await completer.future;
+      expect(response, isNotNull);
+      expect(
+        codec.decodeEnvelope(response!),
+        [true],
+      );
+    });
+  });
+}