Check for touch event queue size before popping.

content/browser/renderer_host/input/touch_event_queue.cc

 // Copyright 2013 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.
 
 #include "content/browser/renderer_host/input/touch_event_queue.h"
 
 #include <utility>
 
 #include "base/auto_reset.h"
 #include "base/macros.h"
@@ skipping 748 matching lines @@
 void TouchEventQueue::PopTouchEventToClient(
     InputEventAckState ack_result,
     const LatencyInfo& renderer_latency_info) {
   AckTouchEventToClient(ack_result, &renderer_latency_info);
 }
 
 void TouchEventQueue::AckTouchEventToClient(
     InputEventAckState ack_result,
     const ui::LatencyInfo* optional_latency_info) {
   DCHECK(!dispatching_touch_ack_);
-  DCHECK(!touch_queue_.empty());
+  if (touch_queue_.empty()) {
+    NOTREACHED() << "Incorrect number of acks";

[mustaq, 2016/09/27 19:53:25]

Nit: "Too many acks"?

+    return;
+  }
   std::unique_ptr<CoalescedWebTouchEvent> acked_event(touch_queue_.front());
   DCHECK(acked_event);
 
   UpdateTouchConsumerStates(acked_event->coalesced_event().event, ack_result);
 
   // Note that acking the touch-event may result in multiple gestures being sent
   // to the renderer, or touch-events being queued.
   base::AutoReset<bool> dispatching_touch_ack(&dispatching_touch_ack_, true);
 
   // Skip ack for TouchScrollStarted since it was synthesized within the queue.
@@ skipping 151 matching lines @@
     if (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED)
       send_touch_events_async_ = false;
     has_handler_for_current_sequence_ |=
         ack_result != INPUT_EVENT_ACK_STATE_NO_CONSUMER_EXISTS;
   } else if (WebTouchEventTraits::IsTouchSequenceEnd(event)) {
     has_handler_for_current_sequence_ = false;
   }
 }
 
 }  // namespace content