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..2056c313ba16838558fa261688b3b7e3b012166f 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
@@ -174,6 +175,20 @@ void InputEventFilter::ForwardToHandler(const IPC::Message& message) {
     return;
   }
 
+  // Send AsyncTouchEvent_ACK for async touch moves, and InputEvent_ACK for
+  // all other types of events.
+  if (event->type == WebInputEvent::TouchMove) {
+    const WebTouchEvent& touch = static_cast<const WebTouchEvent&>(*event);

[jdduke (slow), 2015/03/30 18:04:15]

It sounds like we should consolidate this logic.

What if we have a 

scoped_ptr<IPC::Message> WebInputEventTraits::CreateAckIfNecessary(event)

method which does the right thing? Then both InputEventFilter and RenderWidget
can just call that.

[lanwei, 2015/03/31 13:07:49]

Done.

+    if (!touch.cancelable) {
+      InputHostMsg_HandleUncancelableTouchMoveEvent_ACK_Params ack;
+      SendMessage(
+          scoped_ptr<IPC::Message>(
+              new InputHostMsg_HandleUncancelableTouchMoveEvent_ACK(routing_id,
+                  ack)));
+      return;
+    }
+  }
+
   if (!send_ack)
     return;