Touch Action could cause wheel gestures to be filtered.

content/common/input/synthetic_web_input_event_builders.h

 // 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.
 
 #ifndef CONTENT_COMMON_INPUT_SYNTHETIC_WEB_INPUT_EVENT_BUILDERS_H_
 #define CONTENT_COMMON_INPUT_SYNTHETIC_WEB_INPUT_EVENT_BUILDERS_H_
 
 #include "base/time/time.h"
 #include "content/common/content_export.h"
 #include "third_party/WebKit/public/web/WebInputEvent.h"
@@ skipping 33 matching lines @@
 
 class CONTENT_EXPORT SyntheticWebKeyboardEventBuilder {
  public:
   static blink::WebKeyboardEvent Build(blink::WebInputEvent::Type type);
 };
 
 class CONTENT_EXPORT SyntheticWebGestureEventBuilder {
  public:
   static blink::WebGestureEvent Build(blink::WebInputEvent::Type type,
                                       blink::WebGestureDevice source_device);
-  static blink::WebGestureEvent BuildScrollBegin(float dx_hint,
-                                                 float dy_hint);
+  static blink::WebGestureEvent BuildScrollBegin(
+      float dx_hint,
+      float dy_hint,
+      blink::WebGestureDevice source_device);
   static blink::WebGestureEvent BuildScrollUpdate(
       float dx,
       float dy,
       int modifiers,
       blink::WebGestureDevice source_device);
   static blink::WebGestureEvent BuildPinchUpdate(
       float scale,
       float anchor_x,
       float anchor_y,
       int modifiers,
@@ skipping 17 matching lines @@
   void MovePoint(int index, float x, float y);
   void ReleasePoint(int index);
   void CancelPoint(int index);
 
   void SetTimestamp(base::TimeDelta timestamp);
 };
 
 }  // namespace content
 
 #endif  // CONTENT_COMMON_INPUT_SYNTHETIC_WEB_INPUT_EVENT_BUILDERS_H_