Implement scroll handler latency tracking

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 fe9afc219e6dd30caa9cd94e0c1a3d78f67cf0f2..e9a13fc4f0bb7fa5b0511e1b7d2ec142856d5ff9 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -319,6 +319,7 @@ class CC_EXPORT LayerTreeHostImpl
   bool scroll_affects_scroll_handler() const {
     return scroll_affects_scroll_handler_;
   }
+  void QueueScrollUpdateLatencyInfo(const ui::LatencyInfo& latency_info);
 
   bool IsCurrentlyScrolling() const;
 
@@ -551,6 +552,7 @@ class CC_EXPORT LayerTreeHostImpl
   void MarkUIResourceNotEvicted(UIResourceId uid);
 
   void NotifySwapPromiseMonitorsOfSetNeedsRedraw();
+  void NotifySwapPromiseMonitorsOfForwardingToMainThread();
 
   typedef base::hash_map<UIResourceId, UIResourceData>
       UIResourceMap;
@@ -597,6 +599,7 @@ class CC_EXPORT LayerTreeHostImpl
   bool wheel_scrolling_;
   bool scroll_affects_scroll_handler_;
   int scroll_layer_id_when_mouse_over_scrollbar_;
+  std::vector<ui::LatencyInfo> scroll_update_latency_infos_;
 
   bool tile_priorities_dirty_;