Use WeakPtr for posting cc tasks to main thread

cc/scoped_thread_proxy.h

-// Copyright 2011 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 CC_SCOPED_THREAD_PROXY_H_
-#define CC_SCOPED_THREAD_PROXY_H_
-
-#include "base/memory/ref_counted.h"
-#include "base/callback.h"
-#include "cc/cc_export.h"
-#include "cc/thread.h"
-#include "base/location.h"
-#include "base/logging.h"
-
-namespace cc {
-
-// This class is a proxy used to post tasks to an target thread from any other thread. The proxy may be shut down at
-// any point from the target thread after which no more tasks posted to the proxy will run. In other words, all
-// tasks posted via a proxy are scoped to the lifecycle of the proxy. Use this when posting tasks to an object that
-// might die with tasks in flight.
-//
-// The proxy must be created and shut down from the target thread, tasks may be posted from any thread.
-//
-// Implementation note: Unlike ScopedRunnableMethodFactory in Chromium, pending tasks are not cancelled by actually
-// destroying the proxy. Instead each pending task holds a reference to the proxy to avoid maintaining an explicit
-// list of outstanding tasks.
-class CC_EXPORT ScopedThreadProxy : public base::RefCountedThreadSafe<ScopedThreadProxy> {
-public:
-    static scoped_refptr<ScopedThreadProxy> create(cc::Thread* targetThread)
-    {
-        DCHECK(targetThread->belongsToCurrentThread());
-        return make_scoped_refptr(new ScopedThreadProxy(targetThread));
-    }
-
-    // Can be called from any thread. Posts a task to the target thread that runs unless
-    // shutdown() is called before it runs.
-    void postTask(const tracked_objects::Location& location, base::Closure cb);
-
-    void shutdown();
-
-private:
-    explicit ScopedThreadProxy(cc::Thread* targetThread);
-    friend class base::RefCountedThreadSafe<ScopedThreadProxy>;
-    ~ScopedThreadProxy();
-
-    void runTaskIfNotShutdown(base::Closure cb);
-
-    cc::Thread* m_targetThread;
-    bool m_shutdown; // Only accessed on the target thread
-};
-
-}  // namespace cc
-
-#endif  // CC_SCOPED_THREAD_PROXY_H_