Check for touch event queue size before popping.

content/browser/renderer_host/input/touch_event_queue.cc

Index: content/browser/renderer_host/input/touch_event_queue.cc
diff --git a/content/browser/renderer_host/input/touch_event_queue.cc b/content/browser/renderer_host/input/touch_event_queue.cc
index 701f4fde7fe7e88a6bc5febfeb41b2ecdb277d5a..5aea89905319f5bd1c05089f219950df118a5dad 100644
--- a/content/browser/renderer_host/input/touch_event_queue.cc
+++ b/content/browser/renderer_host/input/touch_event_queue.cc
@@ -766,7 +766,10 @@ 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() << "Too many acks";
+    return;
+  }
   std::unique_ptr<CoalescedWebTouchEvent> acked_event(touch_queue_.front());
   DCHECK(acked_event);