[exp] cc: Introduce cc::CompositorMutator.

content/renderer/gpu/render_widget_compositor.cc

Index: content/renderer/gpu/render_widget_compositor.cc
diff --git a/content/renderer/gpu/render_widget_compositor.cc b/content/renderer/gpu/render_widget_compositor.cc
index 0232eee7ea926a1e6242a8dc5b9c2437986d6062..201805fbdd343432940a1557f15600574a9ad6b7 100644
--- a/content/renderer/gpu/render_widget_compositor.cc
+++ b/content/renderer/gpu/render_widget_compositor.cc
@@ -448,6 +448,8 @@ void RenderWidgetCompositor::Initialize() {
       compositor_deps_->GetSharedBitmapManager();
   gpu::GpuMemoryBufferManager* gpu_memory_buffer_manager =
       compositor_deps_->GetGpuMemoryBufferManager();
+  cc::CompositorMutator* compositor_mutator =
+      compositor_deps_->GetCompositorMutator();
 
   scoped_ptr<cc::BeginFrameSource> external_begin_frame_source;
   if (settings.use_external_begin_frame_source) {
@@ -457,13 +459,14 @@ void RenderWidgetCompositor::Initialize() {
 
   if (compositor_thread_task_runner.get()) {
     layer_tree_host_ = cc::LayerTreeHost::CreateThreaded(
-        this, shared_bitmap_manager, gpu_memory_buffer_manager, settings,
-        main_thread_compositor_task_runner, compositor_thread_task_runner,
-        external_begin_frame_source.Pass());
+        this, shared_bitmap_manager, gpu_memory_buffer_manager,
+        compositor_mutator, settings, main_thread_compositor_task_runner,
+        compositor_thread_task_runner, external_begin_frame_source.Pass());
   } else {
     layer_tree_host_ = cc::LayerTreeHost::CreateSingleThreaded(
-        this, this, shared_bitmap_manager, gpu_memory_buffer_manager, settings,
-        main_thread_compositor_task_runner, external_begin_frame_source.Pass());
+        this, this, shared_bitmap_manager, gpu_memory_buffer_manager,
+        compositor_mutator, settings, main_thread_compositor_task_runner,
+        external_begin_frame_source.Pass());
   }
   DCHECK(layer_tree_host_);
 }