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 6c78d57b0213ecbfbc1ce152e3052783e466807c..f01555a257cd56adde7c78759f8ae93ecb98c303 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
@@ -177,6 +178,19 @@ void InputEventFilter::ForwardToHandler(const IPC::Message& message) {
   if (!send_ack)
     return;
 
+  // Send AsyncTouchEvent_ACK for async touch moves, and InputEvent_ACK for
+  // all other types of events.
+  if (WebInputEvent::isTouchEventType(event->type)) {
+    const WebTouchEvent& touch = static_cast<const WebTouchEvent&>(*event);
+    if (touch.type == WebInputEvent::TouchMove && !touch.cancelable) {
+      InputHostMsg_HandleAsyncTouchEvent_ACK_Params ack;
+      ack.type = event->type;
+      SendMessage(scoped_ptr<IPC::Message>(
+          new InputHostMsg_HandleAsyncTouchEvent_ACK(routing_id, ack)));
+      return;
+    }
+  }
+
   InputHostMsg_HandleInputEvent_ACK_Params ack;
   ack.type = event->type;
   ack.state = ack_state;