Indicate whether a touch event will cause scrolling

content/common/input/web_input_event_traits.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/common/input/web_input_event_traits.h"
 
 #include <bitset>
 #include <limits>
 
 #include "base/logging.h"
@@ skipping 217 matching lines @@
   // correct state, i.e. the touch-points that moved in the last event, but
   // didn't change in the current event, will have Stationary state. It is
   // necessary to change them back to Moved state.
   WebTouchEvent old_event = *event;
   *event = event_to_coalesce;
   for (unsigned i = 0; i < event->touchesLength; ++i) {
     int i_old = GetIndexOfTouchID(old_event, event->touches[i].id);
     if (old_event.touches[i_old].state == blink::WebTouchPoint::StateMoved)
       event->touches[i].state = blink::WebTouchPoint::StateMoved;
   }
+  event->causesScrollingIfUncanceled |=
+      old_event.causesScrollingIfUncanceled;
 }
 
 bool CanCoalesce(const WebGestureEvent& event_to_coalesce,
                  const WebGestureEvent& event) {
   if (event.type != event_to_coalesce.type ||
       event.sourceDevice != event_to_coalesce.sourceDevice ||
       event.modifiers != event_to_coalesce.modifiers)
     return false;
 
   if (event.type == WebInputEvent::GestureScrollUpdate)
@@ skipping 225 matching lines @@
     case WebInputEvent::TouchStart:
     case WebInputEvent::TouchMove:
     case WebInputEvent::TouchEnd:
       return !static_cast<const WebTouchEvent&>(event).cancelable;
     default:
       return false;
   }
 }
 
 }  // namespace content