cc: Split ThreadProxy into ProxyMain and ProxyImpl

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 8312165c1165b6ae8bd1271e106eed1d0f3c04f2..88e9ea55334c4f7adf29da950f2dbe9df7ae5c83 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -41,8 +41,9 @@
 #include "cc/trees/layer_tree_host_common.h"
 #include "cc/trees/layer_tree_host_impl.h"
 #include "cc/trees/layer_tree_impl.h"
+#include "cc/trees/proxy_main.h"
 #include "cc/trees/single_thread_proxy.h"
-#include "cc/trees/thread_proxy.h"
+#include "cc/trees/threaded_channel.h"
 #include "cc/trees/tree_synchronizer.h"
 #include "ui/gfx/geometry/size_conversions.h"
 #include "ui/gfx/geometry/vector2d_conversions.h"
@@ -137,10 +138,13 @@ void LayerTreeHost::InitializeThreaded(
     scoped_refptr<base::SingleThreadTaskRunner> main_task_runner,
     scoped_refptr<base::SingleThreadTaskRunner> impl_task_runner,
     scoped_ptr<BeginFrameSource> external_begin_frame_source) {
-  InitializeProxy(ThreadProxy::Create(this,
-                                      main_task_runner,
-                                      impl_task_runner,
-                                      external_begin_frame_source.Pass()));
+  scoped_ptr<ProxyMain> proxy_main =
+      ProxyMain::Create(this, main_task_runner, impl_task_runner,
+                        external_begin_frame_source.Pass());
+  scoped_ptr<ThreadedChannel> threaded_channel =
+      ThreadedChannel::Create(proxy_main.get());
+  proxy_main->SetChannel(threaded_channel.Pass());
+  InitializeProxy(proxy_main.Pass());
 }
 
 void LayerTreeHost::InitializeSingleThreaded(