re-land the "SourceEventType added to LatencyInfo."

ui/events/blink/web_input_event_traits.h

Index: ui/events/blink/web_input_event_traits.h
diff --git a/ui/events/blink/web_input_event_traits.h b/ui/events/blink/web_input_event_traits.h
index 72c30e4c77ab83a8d44494de3ab4dd1a6f0dd7fb..ea076bef8ca66eed4e5d601ca92ee00ac9dea923 100644
--- a/ui/events/blink/web_input_event_traits.h
+++ b/ui/events/blink/web_input_event_traits.h
@@ -7,6 +7,7 @@
 
 #include "third_party/WebKit/public/platform/WebInputEvent.h"
 #include "ui/events/blink/scoped_web_input_event.h"
+#include "ui/events/latency_info.h"
 
 namespace ui {
 
@@ -23,6 +24,8 @@ class WebInputEventTraits {
 
   // Return uniqueTouchEventId for WebTouchEvent, otherwise return 0.
   static uint32_t GetUniqueTouchEventId(const blink::WebInputEvent& event);
+  static LatencyInfo CreateLatencyInfoForWebGestureEvent(
+      blink::WebGestureEvent event);
 };
 
 }  // namespace ui