Notify Blink about start of gesture scroll through a queued event.

content/common/input/web_touch_event_traits.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.
 
 #include "content/common/input/web_touch_event_traits.h"
 
 #include <stddef.h>
 
 #include "base/logging.h"
 
 using blink::WebInputEvent;
 using blink::WebTouchEvent;
 using blink::WebTouchPoint;
 
 namespace content {
 
 bool WebTouchEventTraits::AllTouchPointsHaveState(
     const WebTouchEvent& event,
     blink::WebTouchPoint::State state) {
   if (!event.touchesLength)
     return false;
   for (size_t i = 0; i < event.touchesLength; ++i) {
     if (event.touches[i].state != state)
       return false;
   }
   return true;
 }
 
 bool WebTouchEventTraits::IsTouchSequenceStart(const WebTouchEvent& event) {
-  DCHECK(event.touchesLength);
+  DCHECK(event.touchesLength ||
+         event.type == WebInputEvent::TouchScrollStarted);
   if (event.type != WebInputEvent::TouchStart)
     return false;
   return AllTouchPointsHaveState(event, blink::WebTouchPoint::StatePressed);
 }
 
 bool WebTouchEventTraits::IsTouchSequenceEnd(const WebTouchEvent& event) {
   if (event.type != WebInputEvent::TouchEnd &&
       event.type != WebInputEvent::TouchCancel)
     return false;
   if (!event.touchesLength)
@@ skipping 36 matching lines @@
       break;
     default:
       NOTREACHED();
       break;
   }
   for (size_t i = 0; i < event->touchesLength; ++i)
     event->touches[i].state = newState;
 }
 
 }  // namespace content