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

cc/trees/layer_tree_host_in_process.h

Index: cc/trees/layer_tree_host_in_process.h
diff --git a/cc/trees/layer_tree_host_in_process.h b/cc/trees/layer_tree_host_in_process.h
index 5eed0099e70a0ea856e241cc67c5390b0c27eb8c..ea91c06aa9d7fe4120537408b1ac2fb3fb0c8565 100644
--- a/cc/trees/layer_tree_host_in_process.h
+++ b/cc/trees/layer_tree_host_in_process.h
@@ -72,6 +72,7 @@ class ResourceUpdateQueue;
 class SharedBitmapManager;
 class TaskGraphRunner;
 struct PendingPageScaleAnimation;
+struct ReflectedMainFrameState;
 struct RenderingStats;
 struct ScrollAndScaleSet;
 
@@ -195,6 +196,13 @@ class CC_EXPORT LayerTreeHostInProcess : public LayerTreeHost {
   void DidCompletePageScaleAnimation();
   void ApplyScrollAndScale(ScrollAndScaleSet* info);
 
+  void SetReflectedMainFrameState(
+      std::unique_ptr<ReflectedMainFrameState> reflected_main_frame_state);
+  const ReflectedMainFrameState* reflected_main_frame_state_for_testing()
+      const {
+    return reflected_main_frame_state_.get();
+  }
+
   LayerTreeHostClient* client() { return client_; }
 
   bool gpu_rasterization_histogram_recorded() const {
@@ -366,6 +374,15 @@ class CC_EXPORT LayerTreeHostInProcess : public LayerTreeHost {
   SurfaceSequenceGenerator surface_sequence_generator_;
   uint32_t num_consecutive_frames_suitable_for_gpu_ = 0;
 
+  // The state that was expected to be reflected from the main thread during
+  // BeginMainFrame, but could not be done. The client provides these deltas
+  // to use during the commit instead of applying them at that point because
+  // its necessary for these deltas to be applied *after* PropertyTrees are
+  // built/updated on the main thread.
+  // TODO(khushalsagar): Investigate removing this after SPV2, since then we
+  // should get these PropertyTrees directly from blink?
+  std::unique_ptr<ReflectedMainFrameState> reflected_main_frame_state_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostInProcess);
 };