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..4f8cd509a252fc629ec53b06d0a8f903f85b24f6 100644
--- a/cc/input/input_handler.h
+++ b/cc/input/input_handler.h
@@ -110,6 +110,14 @@ class CC_EXPORT InputHandler {
     HANDLER_ON_SCROLLING_LAYER
   };
 
+  struct ScrollSourceInfo {
+    enum : uint32_t {

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

Why do you specify the storage type?

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

Done, I made it uint8_t to address the
feedback about info struct size.

+      NONE = 0,
+      SCROLLED_BY_TOUCH = 1 << 0,
+      SCROLLED_BY_WHEEL = 1 << 1,
+    };
+  };
+
   // 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.