Add basic framework for splitting thread proxy.

cc/trees/channel_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_CHANNEL_IMPL_H_
+#define CC_TREES_CHANNEL_IMPL_H_
+
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+// Channel used to send commands to and receive commands from ProxyMain.
+// See channel_main.h
+class CC_EXPORT ChannelImpl {
+ public:
+  // Interface for commands sent to ProxyMain
+  virtual void DidCompleteSwapBuffers() = 0;
+
+ protected:
+  virtual ~ChannelImpl() {}
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_CHANNEL_IMPL_H_