UMA metrics for use count of wheel and touch scrolls.

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 f02a36c93d9f84b42c6df08717ce4986ccd47332..cdfcdab72acf07a235664db3eafcc88c74116d3b 100644
--- a/cc/trees/layer_tree_host_impl.h
+++ b/cc/trees/layer_tree_host_impl.h
@@ -707,6 +707,14 @@ class CC_EXPORT LayerTreeHostImpl
   void ImageDecodeFinished(const base::Callback<void(bool)>& embedder_callback,
                            bool decode_succeeded);
 
+  // This function keeps track of sources of scrolls that are handled in the
+  // compositor side. The information gets shared by the main thread as part of
+  // the begin_main_frame_state. Finally Use counters are updated in the main
+  // thread side to keep track of the frequency of scrolling with different
+  // sources per page load. TODO(crbug.com/691886): Use GRC API to plumb the
+  // scroll source info for Use Counters.
+  void UpdateScrollSourceInfo(bool is_wheel_scroll);
+
   using UIResourceMap = std::unordered_map<UIResourceId, UIResourceData>;
   UIResourceMap ui_resource_map_;
 
@@ -853,6 +861,11 @@ class CC_EXPORT LayerTreeHostImpl
   // begin main frame. These callbacks must only be called on the main thread.
   std::vector<base::Closure> completed_image_decode_callbacks_;
 
+  // These are used to transfer usage of touch and wheel scrolls to the main
+  // thread.
+  bool has_scrolled_by_wheel_;
+  bool has_scrolled_by_touch_;
+
   DISALLOW_COPY_AND_ASSIGN(LayerTreeHostImpl);
 };