Missing source pointer down events are handled.

ui/events/gesture_detection/gesture_detector.h

Index: ui/events/gesture_detection/gesture_detector.h
diff --git a/ui/events/gesture_detection/gesture_detector.h b/ui/events/gesture_detection/gesture_detector.h
index f1366c794761f2244997a82c449ed0838375d2a4..e51f617be166b7be31556628a6cdcb77cda96771 100644
--- a/ui/events/gesture_detection/gesture_detector.h
+++ b/ui/events/gesture_detection/gesture_detector.h
@@ -103,8 +103,8 @@ class GESTURE_DETECTION_EXPORT GestureDetector {
   // pointer ID. This returns nullptr if the source event isn't
   // current_down_event_ or secondary_pointer_down_event_.
   const MotionEvent* GetSourcePointerDownEvent(
-      const MotionEvent& current_down_event,
-      const MotionEvent& secondary_pointer_down_event,
+      const MotionEvent* current_down_event,

[tdresser, 2017/05/11 16:57:27]

We always have a current_down_event, don't we?

[sahel, 2017/05/11 17:26:19]

yes, we do.

+      const MotionEvent* secondary_pointer_down_event,
       const int pointer_id);
 
  private: