CompositorWorkerProxyClientImpl to CompositorProxy cross thread reference is using WeakMember

third_party/WebKit/Source/web/CompositorProxyClientImpl.h

+// Copyright 2017 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CompositorProxyClientImpl_h
+#define CompositorProxyClientImpl_h
+
+#include "core/dom/CompositorProxyClient.h"
+
+namespace blink {
+
+// Registry for CompositorProxies on the control thread.
+// Owned by the control thread.
+class CompositorProxyClientImpl
+    : public GarbageCollectedFinalized<CompositorProxyClientImpl>,
+      public CompositorProxyClient {
+  USING_GARBAGE_COLLECTED_MIXIN(CompositorProxyClientImpl);
+
+ public:
+  DECLARE_TRACE();
+
+  // CompositorProxyClient:
+  void registerCompositorProxy(CompositorProxy*) override;
+  void unregisterCompositorProxy(CompositorProxy*) override;
+
+  HeapHashSet<WeakMember<CompositorProxy>>& proxies() { return m_proxies; }
+
+ private:
+  // CompositorProxy can be constructed in the main thread and control thread.
+  // However this only ever contains ones constructed in the compositor worker
+  // thread.
+  HeapHashSet<WeakMember<CompositorProxy>> m_proxies;
+};
+
+}  // namespace blink
+
+#endif  // CompositorProxyClientImpl_h