UMA metrics for use count of wheel and touch scrolls.

cc/trees/layer_tree_host.cc

Index: cc/trees/layer_tree_host.cc
diff --git a/cc/trees/layer_tree_host.cc b/cc/trees/layer_tree_host.cc
index 7d4b70c5aa0d20625061b4ab508d424632e8a488..34e873e7ede3234cf9500f46b4c7d128a031a3a2 100644
--- a/cc/trees/layer_tree_host.cc
+++ b/cc/trees/layer_tree_host.cc
@@ -737,6 +737,21 @@ void LayerTreeHost::ApplyViewportDeltas(ScrollAndScaleSet* info) {
   SetNeedsUpdateLayers();
 }
 
+void LayerTreeHost::RecordWheelAndTouchScrollingCount(ScrollAndScaleSet* info) {
+  if (!info || info->scroll_source_info == 0)

[danakj, 2017/03/10 20:52:48]

When will info be null?

[sahel, 2017/03/13 20:13:43]

Done.

+    return;
+
+  bool has_scrolled_by_wheel =
+      (info->scroll_source_info &
+       InputHandler::ScrollSourceInfo::SCROLLED_BY_WHEEL) != 0;
+  bool has_scrolled_by_touch =
+      (info->scroll_source_info &
+       InputHandler::ScrollSourceInfo::SCROLLED_BY_TOUCH) != 0;
+
+  client_->RecordWheelAndTouchScrollingCount(has_scrolled_by_wheel,
+                                             has_scrolled_by_touch);
+}
+
 void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
   for (auto& swap_promise : info->swap_promises) {
     TRACE_EVENT_WITH_FLOW1("input,benchmark", "LatencyInfo.Flow",
@@ -767,6 +782,8 @@ void LayerTreeHost::ApplyScrollAndScale(ScrollAndScaleSet* info) {
   // controls from clamping the layout viewport both on the compositor and
   // on the main thread.
   ApplyViewportDeltas(info);
+
+  RecordWheelAndTouchScrollingCount(info);
 }
 
 const base::WeakPtr<InputHandler>& LayerTreeHost::GetInputHandler()