Add a system message channel for controlling the Skia resource cache size (#7257)

See https://github.com/flutter/flutter/issues/25244

shell/common/rasterizer.cc

@@ -360,6 +360,15 @@ void Rasterizer::FireNextFrameCallbackIfPresent() {
   callback();
 }
 
+void Rasterizer::SetResourceCacheMaxBytes(int max_bytes) {
+  GrContext* context = surface_->GetContext();
+  if (context) {
+    int max_resources;
+    context->getResourceCacheLimits(&max_resources, nullptr);
+    context->setResourceCacheLimits(max_resources, max_bytes);
+  }
+}
+
 Rasterizer::Screenshot::Screenshot() {}
 
 Rasterizer::Screenshot::Screenshot(sk_sp<SkData> p_data, SkISize p_size)

shell/common/rasterizer.h

@@ -73,6 +73,8 @@ class Rasterizer final : public blink::SnapshotDelegate {
     return compositor_context_.get();
   }
 
+  void SetResourceCacheMaxBytes(int max_bytes);
+
  private:
   blink::TaskRunners task_runners_;
   std::unique_ptr<Surface> surface_;

shell/common/shell.cc

@@ -33,6 +33,8 @@
 
 namespace shell {
 
+constexpr char kSkiaChannel[] = "flutter/skia";
+
 std::unique_ptr<Shell> Shell::CreateShellOnPlatformThread(
     blink::TaskRunners task_runners,
     blink::Settings settings,
@@ -727,6 +729,11 @@ void Shell::OnEngineHandlePlatformMessage(
   FML_DCHECK(is_setup_);
   FML_DCHECK(task_runners_.GetUITaskRunner()->RunsTasksOnCurrentThread());
 
+  if (message->channel() == kSkiaChannel) {
+    HandleEngineSkiaMessage(std::move(message));
+    return;
+  }
+
   task_runners_.GetPlatformTaskRunner()->PostTask(
       [view = platform_view_->GetWeakPtr(), message = std::move(message)]() {
         if (view) {
@@ -735,6 +742,31 @@ void Shell::OnEngineHandlePlatformMessage(
       });
 }
 
+void Shell::HandleEngineSkiaMessage(
+    fml::RefPtr<blink::PlatformMessage> message) {
+  const auto& data = message->data();
+
+  rapidjson::Document document;
+  document.Parse(reinterpret_cast<const char*>(data.data()), data.size());
+  if (document.HasParseError() || !document.IsObject())
+    return;
+  auto root = document.GetObject();
+  auto method = root.FindMember("method");
+  if (method->value != "Skia.setResourceCacheMaxBytes")
+    return;
+  auto args = root.FindMember("args");
+  if (args == root.MemberEnd() || !args->value.IsInt())
+    return;
+
+  task_runners_.GetGPUTaskRunner()->PostTask(
+      [rasterizer = rasterizer_->GetWeakPtr(),
+       max_bytes = args->value.GetInt()] {
+        if (rasterizer) {
+          rasterizer->SetResourceCacheMaxBytes(max_bytes);
+        }
+      });
+}
+
 // |shell::Engine::Delegate|
 void Shell::OnPreEngineRestart() {
   FML_DCHECK(is_setup_);

shell/common/shell.h

@@ -179,6 +179,8 @@ class Shell final : public PlatformView::Delegate,
   void OnEngineHandlePlatformMessage(
       fml::RefPtr<blink::PlatformMessage> message) override;
 
+  void HandleEngineSkiaMessage(fml::RefPtr<blink::PlatformMessage> message);
+
   // |shell::Engine::Delegate|
   void OnPreEngineRestart() override;