Scroll on main if impl-hit testing isn't guaranteed to be correct

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 b26934548b9454e1252a80a30f0af39252f6b5f3..608003e5ca149ba13883dc553578f5da77374a62 100644
--- a/cc/input/input_handler.h
+++ b/cc/input/input_handler.h
@@ -51,7 +51,14 @@ class CC_EXPORT InputHandlerClient {
 // interface and bind it to the handler on the compositor thread.
 class CC_EXPORT InputHandler {
  public:
-  enum ScrollStatus { ScrollOnMainThread, ScrollStarted, ScrollIgnored };
+  enum ScrollStatus {

[Alexei Svitkine (slow), 2014/04/16 14:24:11]

Nit: Add a comment mentioning these are used in UMA, so they shouldn't be
reordered or existing entries removed.

+    ScrollOnMainThread = 0,
+    ScrollStarted,
+    ScrollIgnored,
+    ScrollUnknown,
+    // This must be the last entry.
+    ScrollStatusCount
+  };
   enum ScrollInputType { Gesture, Wheel, NonBubblingGesture };
 
   // Binds a client to this handler to receive notifications. Only one client