Add basic framework for splitting thread proxy.

cc/trees/proxy_impl.h

+// Copyright 2015 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_TREES_PROXY_IMPL_H_
+#define CC_TREES_PROXY_IMPL_H_
+
+#include "base/memory/weak_ptr.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+// TODO(khushalsagar): The impl side of ThreadProxy. It is currently defined as
+// an interface with the implementation provided by ThreadProxy and will be
+// made an independent class.
+// The methods added to this interface should only use the CompositorThreadOnly
+// variables from ThreadProxy.
+// See crbug/527200
+class CC_EXPORT ProxyImpl {
+ public:
+  // Callback for impl side commands received from the channel.
+  virtual void SetThrottleFrameProductionOnImpl(bool throttle) = 0;
+  virtual void SetLayerTreeHostClientReadyOnImpl() = 0;
+
+  // TODO(khushalsagar): Rename as GetWeakPtr() once ThreadProxy is split.
+  virtual base::WeakPtr<ProxyImpl> GetImplWeakPtr() = 0;
+
+ protected:
+  virtual ~ProxyImpl() {}
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_PROXY_IMPL_H_