gestures: Generate only either scroll-end or fling-start events at the end of a scroll gesture.

ui/views/events/event.h

Index: ui/views/events/event.h
diff --git a/ui/views/events/event.h b/ui/views/events/event.h
index 1a518d35be9a213a2ae99ac59d058de0bbedca48..931441d8ffe5d2c51d43b94c50bf30bbeaf75c2d 100644
--- a/ui/views/events/event.h
+++ b/ui/views/events/event.h
@@ -91,6 +91,11 @@ class VIEWS_EXPORT Event {
            type_ == ui::ET_GESTURE_SCROLL_END;
   }
 
+  bool IsFlingScrollEvent() const {
+    return type_ == ui::ET_SCROLL_FLING_CANCEL ||
+           type_ == ui::ET_SCROLL_FLING_START;
+  }
+
  protected:
   Event(ui::EventType type, int flags);
   Event(const NativeEvent& native_event, ui::EventType type, int flags);