Coalesce async touch move events until the ack back from render

content/renderer/render_widget.cc

Index: content/renderer/render_widget.cc
diff --git a/content/renderer/render_widget.cc b/content/renderer/render_widget.cc
index 17733e0439c92402cbc95896bcc0ca896fa342e2..a0d534b91a8988d0fd1b0c1e508f246be4d8fdfd 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -1225,13 +1225,10 @@ void RenderWidget::OnHandleInputEvent(const blink::WebInputEvent* input_event,
   // by reentrant calls for events after the paused one.
   bool no_ack = ignore_ack_for_mouse_move_from_debugger_ &&
       input_event->type == WebInputEvent::MouseMove;
-  if (!WebInputEventTraits::IgnoresAckDisposition(*input_event) && !no_ack) {
-    InputHostMsg_HandleInputEvent_ACK_Params ack;
-    ack.type = input_event->type;
-    ack.state = ack_result;
-    ack.latency = swap_latency_info;
-    scoped_ptr<IPC::Message> response(
-        new InputHostMsg_HandleInputEvent_ACK(routing_id_, ack));
+  scoped_ptr<IPC::Message> response = WebInputEventTraits::CreateAckIfNecessary(
+      *input_event, ack_result, swap_latency_info, NULL, routing_id_);
+
+  if (!no_ack && response) {
     if (rate_limiting_wanted && frame_pending && !is_hidden_) {
       // We want to rate limit the input events in this case, so we'll wait for
       // painting to finish before ACKing this message.