Split ThreadProxy methods to ProxyMain and ProxyImpl.

cc/trees/proxy_common.cc

Index: cc/trees/proxy_common.cc
diff --git a/cc/trees/proxy_common.cc b/cc/trees/proxy_common.cc
new file mode 100644
index 0000000000000000000000000000000000000000..f047e8ea8fec106625fab319073a15e8c3361cba
--- /dev/null
+++ b/cc/trees/proxy_common.cc
@@ -0,0 +1,15 @@
+// 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.
+
+#include "cc/trees/proxy_common.h"
+#include "cc/trees/layer_tree_host.h"
+
+namespace cc {
+
+BeginMainFrameAndCommitState::BeginMainFrameAndCommitState()
+    : memory_allocation_limit_bytes(0), evicted_ui_resources(false) {}
+
+BeginMainFrameAndCommitState::~BeginMainFrameAndCommitState() {}
+
+}  // namespace cc