Coalesce async touch move events until the ack back from render

content/browser/renderer_host/input/input_router_impl.cc

Index: content/browser/renderer_host/input/input_router_impl.cc
diff --git a/content/browser/renderer_host/input/input_router_impl.cc b/content/browser/renderer_host/input/input_router_impl.cc
index 54bf892014c80b6884e624cdcdaac312c0817e46..ebe00d2cb21dd361014a5bdf07203f234d5869a7 100644
--- a/content/browser/renderer_host/input/input_router_impl.cc
+++ b/content/browser/renderer_host/input/input_router_impl.cc
@@ -248,6 +248,8 @@ bool InputRouterImpl::OnMessageReceived(const IPC::Message& message) {
   bool handled = true;
   IPC_BEGIN_MESSAGE_MAP(InputRouterImpl, message)
     IPC_MESSAGE_HANDLER(InputHostMsg_HandleInputEvent_ACK, OnInputEventAck)
+    IPC_MESSAGE_HANDLER(InputHostMsg_HandleAsyncTouchEvent_ACK,
+                        OnAsyncTouchEventAck)
     IPC_MESSAGE_HANDLER(InputHostMsg_DidOverscroll, OnDidOverscroll)
     IPC_MESSAGE_HANDLER(InputHostMsg_MoveCaret_ACK, OnMsgMoveCaretAck)
     IPC_MESSAGE_HANDLER(InputHostMsg_SelectRange_ACK, OnSelectMessageAck)
@@ -347,13 +349,19 @@ void InputRouterImpl::OfferToHandlers(const WebInputEvent& input_event,
   // Touch events should always indicate in the event whether they are
   // cancelable (respect ACK disposition) or not.
   bool ignores_ack = WebInputEventTraits::IgnoresAckDisposition(input_event);
+  bool is_async_touch_move = false;
   if (WebInputEvent::isTouchEventType(input_event.type)) {
     const WebTouchEvent& touch = static_cast<const WebTouchEvent&>(input_event);
-    DCHECK_NE(ignores_ack, !!touch.cancelable);
+    if (touch.type == WebInputEvent::TouchMove && !touch.cancelable)
+      is_async_touch_move = true;
+
+    if (touch.type != WebInputEvent::TouchMove)
+      DCHECK_NE(ignores_ack, touch.cancelable);
   }
 
-  // If we don't care about the ack disposition, send the ack immediately.
-  if (ignores_ack) {
+  // If we don't care about the ack disposition, or it is an async touchmove
+  // event, send the ack immediately.
+  if (ignores_ack || is_async_touch_move) {
     ProcessInputEventAck(input_event.type,
                          INPUT_EVENT_ACK_STATE_IGNORED,
                          latency_info,
@@ -435,6 +443,15 @@ void InputRouterImpl::OnInputEventAck(
       Details<int>(&type));
 }
 
+void InputRouterImpl::OnAsyncTouchEventAck(
+    const InputHostMsg_HandleAsyncTouchEvent_ACK_Params& ack) {
+  ProcessAsyncTouchAck();
+  int type = static_cast<int>(ack.type);
+  NotificationService::current()->Notify(
+      NOTIFICATION_RENDER_WIDGET_HOST_DID_RECEIVE_INPUT_EVENT_ACK,
+      Source<void>(this), Details<int>(&type));
+}
+
 void InputRouterImpl::OnDidOverscroll(const DidOverscrollParams& params) {
   client_->DidOverscroll(params);
 }
@@ -597,6 +614,10 @@ void InputRouterImpl::ProcessTouchAck(
   touch_event_queue_.ProcessTouchAck(ack_result, latency);
 }
 
+void InputRouterImpl::ProcessAsyncTouchAck() {
+  touch_event_queue_.ProcessAsyncTouchAck();
+}
+
 void InputRouterImpl::UpdateTouchAckTimeoutEnabled() {
   // Mobile sites tend to be well-behaved with respect to touch handling, so
   // they have less need for the touch timeout fallback.