Add basic framework for splitting thread proxy.

cc/trees/proxy_main.h

Index: cc/trees/proxy_main.h
diff --git a/cc/trees/proxy_main.h b/cc/trees/proxy_main.h
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+++ b/cc/trees/proxy_main.h
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+// 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_MAIN_H_
+#define CC_TREES_PROXY_MAIN_H_
+
+#include "base/memory/weak_ptr.h"
+#include "cc/base/cc_export.h"
+
+namespace cc {
+class ThreadedChannel;
+
+// TODO(khushalsagar): The main 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 MainThreadOnly or
+// BlockedMainThread variables from ThreadProxy.
+// See crbug/527200.
+class CC_EXPORT ProxyMain {
+ public:
+  // TODO(khushalsagar): Make this ChannelMain*. When ProxyMain and
+  // ProxyImpl are split, ProxyImpl will be passed a reference to ChannelImpl
+  // at creation. Right now we just set it directly from ThreadedChannel
+  // when the impl side is initialized.
+  virtual void SetChannel(scoped_ptr<ThreadedChannel> threaded_channel) = 0;
+
+  // Callback for main side commands received from the Channel.
+  virtual void DidCompleteSwapBuffers() = 0;
+
+  // TODO(khushalsagar): Rename as GetWeakPtr() once ThreadProxy is split.
+  virtual base::WeakPtr<ProxyMain> GetMainWeakPtr() = 0;
+
+ protected:
+  virtual ~ProxyMain() {}
+};
+
+}  // namespace cc
+
+#endif  // CC_TREES_PROXY_MAIN_H_