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 e3c2602b74c8bdd7d6976db1f6e2ee47f5720cf1..56508222adb364ab6ee0a0a13436b685b202dd8c 100644
--- a/content/renderer/render_widget.cc
+++ b/content/renderer/render_widget.cc
@@ -1225,12 +1225,30 @@ void RenderWidget::OnHandleInputEvent(const blink::WebInputEvent* input_event,
   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));
+    // Send AsyncTouchEvent_ACK for async touch moves, and InputEvent_ACK for
+    // all other types of events.
+    scoped_ptr<IPC::Message> response;
+    bool is_async_touch_move = false;
+    if (WebInputEvent::isTouchEventType(input_event->type)) {
+      const WebTouchEvent& touch =
+          static_cast<const WebTouchEvent&>(*input_event);
+      if (touch.type == WebInputEvent::TouchMove && !touch.cancelable)
+        is_async_touch_move = true;
+    }
+    if (is_async_touch_move) {
+      InputHostMsg_HandleAsyncTouchEvent_ACK_Params ack;
+      ack.type = input_event->type;
+      response = scoped_ptr<IPC::Message>(
+          new InputHostMsg_HandleAsyncTouchEvent_ACK(routing_id_, ack));
+    } else {
+      InputHostMsg_HandleInputEvent_ACK_Params ack;
+      ack.type = input_event->type;
+      ack.state = ack_result;
+      ack.latency = swap_latency_info;
+      response = scoped_ptr<IPC::Message>(
+          new InputHostMsg_HandleInputEvent_ACK(routing_id_, ack));
+    }
+
     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.