Missing source pointer down events are handled.

ui/events/gesture_detection/gesture_detector.cc

 // 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.
 
 // MSVC++ requires this to be set before any other includes to get M_PI.
 #define _USE_MATH_DEFINES
 
 #include "ui/events/gesture_detection/gesture_detector.h"
 
 #include <stddef.h>
@@ skipping 228 matching lines @@
           velocity_tracker_.Clear();
           break;
         }
         vx_total += vx2;
         vy_total += vy2;
       }
 
       handled = HandleSwipeIfNeeded(ev, vx_total / count, vy_total / count);
 
       if (two_finger_tap_allowed_for_gesture_ && ev.GetPointerCount() == 2 &&
+          secondary_pointer_down_event_ &&
           (ev.GetEventTime() - secondary_pointer_down_event_->GetEventTime() <=
            two_finger_tap_timeout_)) {
         handled = listener_->OnTwoFingerTap(*current_down_event_, ev);
       }
       two_finger_tap_allowed_for_gesture_ = false;
     } break;
 
     case MotionEvent::ACTION_DOWN: {
       bool is_repeated_tap =
           current_down_event_ && previous_up_event_ &&
@@ skipping 288 matching lines @@
 
 bool GestureDetector::IsWithinTouchSlop(const MotionEvent& ev) {
   // If there have been more than two down pointers in the touch sequence,
   // tapping is not possible. Slop region check is not needed.
   if (maximum_pointer_count_ > 2)
     return false;
 
   for (size_t i = 0; i < ev.GetPointerCount(); i++) {
     const int pointer_id = ev.GetPointerId(i);
     const MotionEvent* source_pointer_down_event = GetSourcePointerDownEvent(
-        *current_down_event_,
-        (maximum_pointer_count_ > 1 && secondary_pointer_down_event_)
-            ? *secondary_pointer_down_event_
-            : *current_down_event_,
+        *current_down_event_.get(), secondary_pointer_down_event_.get(),
         pointer_id);
-    DCHECK(source_pointer_down_event);
+
     if (!source_pointer_down_event)
       return false;
 
     int source_index =
         source_pointer_down_event->FindPointerIndexOfId(pointer_id);
     DCHECK_GE(source_index, 0);
     if (source_index < 0)
       return false;
 
     float dx = source_pointer_down_event->GetX(source_index) - ev.GetX(i);
     float dy = source_pointer_down_event->GetY(source_index) - ev.GetY(i);
     if (dx * dx + dy * dy > touch_slop_square_)
       return false;
   }
 
   return true;
 }
 
 const MotionEvent* GestureDetector::GetSourcePointerDownEvent(
     const MotionEvent& current_down_event,
-    const MotionEvent& secondary_pointer_down_event,
+    const MotionEvent* secondary_pointer_down_event,
     const int pointer_id) {
   if (current_down_event.GetPointerId(0) == pointer_id)
     return &current_down_event;
 
-  for (size_t i = 0; i < secondary_pointer_down_event.GetPointerCount(); i++) {
-    if (secondary_pointer_down_event.GetPointerId(i) == pointer_id)
-      return &secondary_pointer_down_event;
+  // Secondary pointer down event is sometimes missing (crbug.com/704426), the
+  // source pointer down event is not found in these cases.
+  // crbug.com/704426 is the only related bug report and we don't have any
+  // reliable repro of the bug.
+  if (!secondary_pointer_down_event)
+    return nullptr;
+
+  for (size_t i = 0; i < secondary_pointer_down_event->GetPointerCount(); i++) {
+    if (secondary_pointer_down_event->GetPointerId(i) == pointer_id)
+      return secondary_pointer_down_event;
   }
 
-  NOTREACHED();
   return nullptr;
 }
 
 }  // namespace ui