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 433d5cfd74c9ece7d8cd5e507db4a95ea383d53b..22572527694bddbe8bea7b6e70d96051de45696a 100644
--- a/ui/views/events/event.h
+++ b/ui/views/events/event.h
@@ -94,6 +94,11 @@ 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);