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

third_party/WebKit/Source/web/PageWidgetDelegate.cpp

 /*
  * Copyright (C) 2012 Google Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions are
  * met:
  *
  *     * Redistributions of source code must retain the above copyright
  * notice, this list of conditions and the following disclaimer.
  *     * Redistributions in binary form must reproduce the above
@@ skipping 151 matching lines @@
     case WebInputEvent::GestureDoubleTap:
     case WebInputEvent::GestureTwoFingerTap:
     case WebInputEvent::GestureLongPress:
     case WebInputEvent::GestureLongTap:
         return handler.handleGestureEvent(static_cast<const WebGestureEvent&>(event));
 
     case WebInputEvent::TouchStart:
     case WebInputEvent::TouchMove:
     case WebInputEvent::TouchEnd:
     case WebInputEvent::TouchCancel:
+    case WebInputEvent::TouchScrollStarted:
         if (!root || !root->view())
             return WebInputEventResult::NotHandled;
         return handler.handleTouchEvent(*root, static_cast<const WebTouchEvent&>(event));
     case WebInputEvent::GesturePinchBegin:
     case WebInputEvent::GesturePinchEnd:
     case WebInputEvent::GesturePinchUpdate:
         // Touchscreen pinch events are currently not handled in main thread. Once they are,
         // these should be passed to |handleGestureEvent| similar to gesture scroll events.
         return WebInputEventResult::NotHandled;
     default:
@@ skipping 71 matching lines @@
         WEBINPUT_EVENT_CASE(TouchMove)
         WEBINPUT_EVENT_CASE(TouchEnd)
         WEBINPUT_EVENT_CASE(TouchCancel)
     default:
         NOTREACHED();
         return "";
     }
 }
 
 } // namespace blink