[exp] cc: Introduce cc::CompositorMutator.

content/test/fake_compositor_dependencies.cc

 // Copyright 2014 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/test/fake_compositor_dependencies.h"
 
 #include "base/message_loop/message_loop_proxy.h"
 #include "cc/test/fake_external_begin_frame_source.h"
 #include "third_party/khronos/GLES2/gl2.h"
 
@@ skipping 63 matching lines @@
 
 cc::SharedBitmapManager* FakeCompositorDependencies::GetSharedBitmapManager() {
   return &shared_bitmap_manager_;
 }
 
 gpu::GpuMemoryBufferManager*
 FakeCompositorDependencies::GetGpuMemoryBufferManager() {
   return &gpu_memory_buffer_manager_;
 }
 
+cc::CompositorMutator* FakeCompositorDependencies::GetCompositorMutator() {
+  return nullptr;
+}
+
 RendererScheduler* FakeCompositorDependencies::GetRendererScheduler() {
   return &renderer_scheduler_;
 }
 
 cc::ContextProvider*
 FakeCompositorDependencies::GetSharedMainThreadContextProvider() {
   NOTREACHED();
   return nullptr;
 }
 
 scoped_ptr<cc::BeginFrameSource>
 FakeCompositorDependencies::CreateExternalBeginFrameSource(int routing_id) {
   double refresh_rate = 200.0;
   return make_scoped_ptr(new cc::FakeExternalBeginFrameSource(refresh_rate));
 }
 
 }  // namespace content