Missing source pointer down events are handled.

ui/events/gesture_detection/gesture_detector.h

 // Copyright 2014 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef UI_EVENTS_GESTURE_DETECTION_GESTURE_DETECTOR_H_
 #define UI_EVENTS_GESTURE_DETECTION_GESTURE_DETECTOR_H_
 
 #include <memory>
 
 #include "base/logging.h"
@@ skipping 85 matching lines @@
 
   bool is_double_tapping() const { return is_double_tapping_; }
 
   void set_longpress_enabled(bool enabled) { longpress_enabled_ = enabled; }
   void set_showpress_enabled(bool enabled) { showpress_enabled_ = enabled; }
 
   // Returns the event storing the initial position of the pointer with given
   // 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:
   void Init(const Config& config);
   void OnShowPressTimeout();
   void OnLongPressTimeout();
   void OnTapTimeout();
   void Cancel();
   void CancelTaps();
   bool IsRepeatedTap(const MotionEvent& first_down,
@@ skipping 60 matching lines @@
 
   // Determines speed during touch scrolling.
   VelocityTrackerState velocity_tracker_;
 
   DISALLOW_COPY_AND_ASSIGN(GestureDetector);
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_GESTURE_DETECTION_GESTURE_DETECTOR_H_