Events ignoring ack disposition receive synthetic acks.

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 "base/logging.h"
 
 using blink::WebGestureEvent;
 using blink::WebInputEvent;
@@ skipping 265 matching lines @@
                event_to_coalesce,
                &event);
 }
 
 void WebInputEventTraits::Coalesce(const WebInputEvent& event_to_coalesce,
                                    WebInputEvent* event) {
   DCHECK(event);
   Apply(WebInputEventCoalesce(), event->type, event_to_coalesce, event);
 }
 
+bool WebInputEventTraits::IgnoresAckDisposition(
+    blink::WebInputEvent::Type type) {
+  return type == WebInputEvent::GestureTapDown ||
+      type == WebInputEvent::GestureShowPress ||
+      type == WebInputEvent::GestureTapCancel;
+}
+
 }  // namespace content