UMA metrics for use count of wheel and touch scrolls.

cc/input/input_handler.h

Index: cc/input/input_handler.h
diff --git a/cc/input/input_handler.h b/cc/input/input_handler.h
index 7e6124c0a07297a9461a81bc7950a0e31b9dd13b..04457623cfc0553f8982bff3d79607de801ba469 100644
--- a/cc/input/input_handler.h
+++ b/cc/input/input_handler.h
@@ -110,6 +110,13 @@ class CC_EXPORT InputHandler {
     HANDLER_ON_SCROLLING_LAYER
   };
 
+  enum ScrollSourceInfo {
+    NONE,
+    SCROLLED_BY_TOUCH,

[bokan, 2017/03/09 17:31:03]

Make this a bitfield. i.e. SCROLLED_BY_TOUCH = 0x1, SCROLLED_BY_WHEEL = 0x2.
That way you can avoid the awkward translation in
LayerTreeHostImpl::UpdateScrollSourceInfo and just OR the values together.

[sahel, 2017/03/10 16:21:33]

Done.

+    SCROLLED_BY_WHEEL,
+    SCROLLED_BY_TOUCH_AND_WHEEL,
+  };
+
   // Binds a client to this handler to receive notifications. Only one client
   // can be bound to an InputHandler. The client must live at least until the
   // handler calls WillShutdown() on the client.