Coalesce async touch move events until the ack back from render

content/renderer/input/input_event_filter.cc

Index: content/renderer/input/input_event_filter.cc
diff --git a/content/renderer/input/input_event_filter.cc b/content/renderer/input/input_event_filter.cc
index 180be389354052d41f59adf08e1000f71da72ef9..22d0fc01b7d337b1cf85c6a6c274b6ee241dc354 100644
--- a/content/renderer/input/input_event_filter.cc
+++ b/content/renderer/input/input_event_filter.cc
@@ -21,6 +21,7 @@
 #include "ui/gfx/geometry/vector2d_f.h"
 
 using blink::WebInputEvent;
+using blink::WebTouchEvent;
 
 #include "ipc/ipc_message_null_macros.h"
 #undef IPC_MESSAGE_DECL
@@ -150,7 +151,7 @@ void InputEventFilter::ForwardToHandler(const IPC::Message& message) {
   bool is_keyboard_shortcut = get<2>(params);
   DCHECK(event);
 
-  const bool send_ack = !WebInputEventTraits::IgnoresAckDisposition(*event);
+  const bool send_ack = WebInputEventTraits::WillReceiveAckFromRenderer(*event);
 
   // Intercept |DidOverscroll| notifications, bundling any triggered overscroll
   // response with the input event ack.
@@ -173,16 +174,10 @@ void InputEventFilter::ForwardToHandler(const IPC::Message& message) {
     return;
   }
 
-  if (!send_ack)
-    return;
-
-  InputHostMsg_HandleInputEvent_ACK_Params ack;
-  ack.type = event->type;
-  ack.state = ack_state;
-  ack.latency = latency_info;
-  ack.overscroll = overscroll_params.Pass();
-  SendMessage(scoped_ptr<IPC::Message>(
-      new InputHostMsg_HandleInputEvent_ACK(routing_id, ack)));
+  scoped_ptr<IPC::Message> response = WebInputEventTraits::CreateAckIfNecessary(
+      *event, ack_state, latency_info, overscroll_params.Pass(), routing_id);
+  if (response)
+    SendMessage(response.Pass());
 }
 
 void InputEventFilter::SendMessage(scoped_ptr<IPC::Message> message) {