Add UMA/Telemetry stats for end-to-end scroll latency

ui/base/latency_info.h

Index: ui/base/latency_info.h
diff --git a/ui/base/latency_info.h b/ui/base/latency_info.h
index 423182a0379ea382d9b40cda4c231511904750ff..862e730418cb74c25be4108a5d4a38b3dca24367 100644
--- a/ui/base/latency_info.h
+++ b/ui/base/latency_info.h
@@ -24,6 +24,7 @@ enum LatencyComponentType {
   // events is sent from RWH to renderer. In non-aura platform,
   // INPUT_EVENT_LATENCY_RWH_COMPONENT is the same as
   // INPUT_EVENT_LATENCY_INJECTED_RWH_COMPONENT.
+  // It is now only set for GestureScrollXXX events.

[Rick Byers, 2013/07/10 01:36:30]

Please just rename this to 'GestureScroll' instead of 'Injected' and update the
comments accordingly.  I think the code that looks for this will make more sense
then.

[Yufeng Shen (Slow to review), 2013/07/10 15:12:04]

Done.

   INPUT_EVENT_LATENCY_INJECTED_RWH_COMPONENT,
   // Original timestamp for input event (e.g. timestamp from kernel).
   INPUT_EVENT_LATENCY_ORIGINAL_COMPONENT,