Add basic framework for splitting thread proxy.

cc/trees/channel_main.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_MAIN_H_
+#define CC_TREES_CHANNEL_MAIN_H_
+
+#include "cc/base/cc_export.h"
+
+namespace cc {
+
+// ChannelMain and ChannelImpl provide an abstract communication layer for
+// the main and impl side of the compositor.
+//
+// The communication sequence between the 2 sides is:
+//
+// LayerTreeHost<-->ProxyMain<-->ChannelMain
+//                                      |
+//                                      |
+//                               ChannelImpl<-->ProxyImpl<-->LayerTreeHostImpl
+
+class CC_EXPORT ChannelMain {
+ public:
+  // Interface for commands sent to the ProxyImpl
+  virtual void SetThrottleFrameProductionOnImpl(bool throttle) = 0;
+  virtual void SetLayerTreeHostClientReadyOnImpl() = 0;
+
+  virtual ~ChannelMain() {}
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_CHANNEL_MAIN_H_