cc:: Add remote mode to the compositor

cc/proto/compositor_message_to_main.proto

 // 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.
 
 syntax = "proto2";
 
 option optimize_for = LITE_RUNTIME;
 
 package cc.proto;
 
-message Point3F {
-  optional float x = 1;
-  optional float y = 2;
-  optional float z = 3;
+// Control messages sent to the main side of the compositor on the engine.
+message CompositorMessageToMain {
+  // TODO(khushalsagar): Add messages sent to the main compositor from the impl
+  // side.
 }