cc/blimp: Add synchronization for scroll/scale state.

cc/trees/layer_tree_impl.h

Index: cc/trees/layer_tree_impl.h
diff --git a/cc/trees/layer_tree_impl.h b/cc/trees/layer_tree_impl.h
index 620d04257013d4e42090d096b52430e420039f6d..7eae2c224c913e05d6c34e5f66ff07c3291816a6 100644
--- a/cc/trees/layer_tree_impl.h
+++ b/cc/trees/layer_tree_impl.h
@@ -51,6 +51,7 @@ class TileManager;
 class UIResourceRequest;
 class VideoFrameControllerClient;
 struct PendingPageScaleAnimation;
+struct ReflectedMainFrameState;
 
 typedef std::vector<UIResourceRequest> UIResourceRequestQueue;
 typedef SyncedProperty<AdditionGroup<float>> SyncedTopControls;
@@ -159,6 +160,10 @@ class CC_EXPORT LayerTreeImpl {
     return source_frame_number_ != is_first_frame_after_commit_tracker_;
   }
 
+  void SetReflectedMainFrameState(
+      std::unique_ptr<ReflectedMainFrameState> reflected_main_frame_state);
+  void ApplyReflectedMainFrameState();
+
   void set_is_first_frame_after_commit(bool is_first_frame_after_commit) {
     is_first_frame_after_commit_tracker_ =
         is_first_frame_after_commit ? -1 : source_frame_number_;
@@ -562,6 +567,8 @@ class CC_EXPORT LayerTreeImpl {
 
   std::unique_ptr<PendingPageScaleAnimation> pending_page_scale_animation_;
 
+  std::unique_ptr<ReflectedMainFrameState> reflected_main_frame_state_;
+
  private:
   DISALLOW_COPY_AND_ASSIGN(LayerTreeImpl);
 };