Touch Action could cause wheel gestures to be filtered.

content/common/input/synthetic_web_input_event_builders.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/synthetic_web_input_event_builders.h"
 
 #include "base/logging.h"
 #include "content/common/input/web_touch_event_traits.h"
 #include "ui/events/base_event_utils.h"
 #include "ui/events/keycodes/keyboard_codes.h"
@@ skipping 100 matching lines @@
       type == WebInputEvent::GestureDoubleTap) {
     result.data.tap.tapCount = 1;
     result.data.tap.width = 10;
     result.data.tap.height = 10;
   }
   return result;
 }
 
 WebGestureEvent SyntheticWebGestureEventBuilder::BuildScrollBegin(
     float dx_hint,
-    float dy_hint) {
-  WebGestureEvent result = Build(WebInputEvent::GestureScrollBegin,
-                                 blink::WebGestureDeviceTouchscreen);
+    float dy_hint,
+    blink::WebGestureDevice source_device) {
+  WebGestureEvent result =
+      Build(WebInputEvent::GestureScrollBegin, source_device);
   result.data.scrollBegin.deltaXHint = dx_hint;
   result.data.scrollBegin.deltaYHint = dy_hint;
   return result;
 }
 
 WebGestureEvent SyntheticWebGestureEventBuilder::BuildScrollUpdate(
     float dx,
     float dy,
     int modifiers,
     blink::WebGestureDevice source_device) {
@@ skipping 100 matching lines @@
   touches[index].state = WebTouchPoint::StateCancelled;
   WebTouchEventTraits::ResetType(
       WebInputEvent::TouchCancel, timeStampSeconds, this);
 }
 
 void SyntheticWebTouchEvent::SetTimestamp(base::TimeDelta timestamp) {
   timeStampSeconds = timestamp.InSecondsF();
 }
 
 }  // namespace content