[exp] cc: Introduce cc::CompositorMutator.

content/renderer/render_thread_impl.cc

 // Copyright (c) 2012 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 "content/renderer/render_thread_impl.h"
 
 #include <algorithm>
 #include <limits>
 #include <map>
 #include <vector>
@@ skipping 1378 matching lines @@
 
 scoped_refptr<base::SingleThreadTaskRunner>
 RenderThreadImpl::GetCompositorImplThreadTaskRunner() {
   return compositor_message_loop_proxy_;
 }
 
 gpu::GpuMemoryBufferManager* RenderThreadImpl::GetGpuMemoryBufferManager() {
   return gpu_memory_buffer_manager();
 }
 
+cc::CompositorMutator* RenderThreadImpl::GetCompositorMutator() {
+  return nullptr;
+}
+
 RendererScheduler* RenderThreadImpl::GetRendererScheduler() {
   return renderer_scheduler_.get();
 }
 
 cc::ContextProvider* RenderThreadImpl::GetSharedMainThreadContextProvider() {
   return SharedMainThreadContextProvider().get();
 }
 
 scoped_ptr<cc::BeginFrameSource>
 RenderThreadImpl::CreateExternalBeginFrameSource(int routing_id) {
@@ skipping 402 matching lines @@
 }
 
 void RenderThreadImpl::PendingRenderFrameConnect::OnConnectionError() {
   size_t erased =
       RenderThreadImpl::current()->pending_render_frame_connects_.erase(
           routing_id_);
   DCHECK_EQ(1u, erased);
 }
 
 }  // namespace content