compositor-worker: cc->blink mutation plumbing

cc/trees/layer_tree_host_impl.h

Index: cc/trees/layer_tree_host_impl.h
diff --git a/cc/trees/layer_tree_host_impl.h b/cc/trees/layer_tree_host_impl.h
index cb7b9cfe71b5d4e2a30310c73bec88ecfdb85e48..52d01fac1a6d793d82f676a2e918d4fb16651f2b 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -12,6 +12,7 @@
 #include <unordered_map>
 #include <vector>
 
+#include "base/callback.h"
 #include "base/macros.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
@@ -79,6 +80,8 @@ class UIResourceRequest;
 struct ScrollAndScaleSet;
 class Viewport;
 
+using BeginFrameCallbackList = std::vector<base::Closure>;
+
 enum class GpuRasterizationStatus {
   ON,
   ON_FORCED,
@@ -457,6 +460,8 @@ class CC_EXPORT LayerTreeHostImpl
 
   const gfx::Transform& DrawTransform() const;
 
+  scoped_ptr<BeginFrameCallbackList> ProcessLayerTreeMutations();
+
   scoped_ptr<ScrollAndScaleSet> ProcessScrollDeltas();
 
   void set_max_memory_needed_bytes(size_t bytes) {