Events ignoring ack disposition receive synthetic acks.

content/common/input/web_input_event_traits.cc

Index: content/common/input/web_input_event_traits.cc
diff --git a/content/common/input/web_input_event_traits.cc b/content/common/input/web_input_event_traits.cc
index 48787a298c844e0e3841964e4a3a0646c937c91e..08d66ba68158b59660ccf789376ae1b4aea37ea1 100644
--- a/content/common/input/web_input_event_traits.cc
+++ b/content/common/input/web_input_event_traits.cc
@@ -283,4 +283,11 @@ void WebInputEventTraits::Coalesce(const WebInputEvent& event_to_coalesce,
   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