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..d832f83cfe6e5909d7bde27dcc829ff444c6d083 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_HandleUncancelableTouchMoveEvent_ACK,
+                        OnUncancelableTouchMoveAck)
     IPC_MESSAGE_HANDLER(InputHostMsg_DidOverscroll, OnDidOverscroll)
     IPC_MESSAGE_HANDLER(InputHostMsg_MoveCaret_ACK, OnMsgMoveCaretAck)
     IPC_MESSAGE_HANDLER(InputHostMsg_SelectRange_ACK, OnSelectMessageAck)
@@ -349,7 +351,7 @@ void InputRouterImpl::OfferToHandlers(const WebInputEvent& input_event,
   bool ignores_ack = WebInputEventTraits::IgnoresAckDisposition(input_event);
   if (WebInputEvent::isTouchEventType(input_event.type)) {
     const WebTouchEvent& touch = static_cast<const WebTouchEvent&>(input_event);
-    DCHECK_NE(ignores_ack, !!touch.cancelable);
+    DCHECK_NE(ignores_ack, touch.cancelable);
   }
 
   // If we don't care about the ack disposition, send the ack immediately.
@@ -435,6 +437,10 @@ void InputRouterImpl::OnInputEventAck(
       Details<int>(&type));
 }
 
+void InputRouterImpl::OnUncancelableTouchMoveAck() {
+  touch_event_queue_.ProcessUncancelableTouchMoveAck();
+}
+
 void InputRouterImpl::OnDidOverscroll(const DidOverscrollParams& params) {
   client_->DidOverscroll(params);
 }