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 {
+class ThreadProxy;

[David Trainor- moved to gerrit, 2015/09/23 17:54:11]

Remove?

[Khushal, 2015/09/23 20:50:28]

Done.

+
+// 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

[David Trainor- moved to gerrit, 2015/09/23 17:54:11]

Odd formatting request, but can we line these two top level arrow blocks up?

Also, it might be good to show that for things like blimp the channels talk to
each other.  The ThreadedChannel case is a bit special because ChannelMain and
ChannelImpl are the same thing.

[Khushal, 2015/09/23 20:50:28]

Done. Added ChannelImpl in the communication sequence. I suppose we can define
the special case of ThreadedChannel in the comments on ThreadedChannel.h.

+//                                      |
+//                                      |
+//                                    ProxyImpl --> LayerTreeHostImpl
+//
+// LayerTreeHostImpl --> ProxyImpl --> ChannelImpl
+//                                      |
+//                                      |
+//                                    ProxyMain --> LayerTreeHost
+
+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_