Don't send touch move to renderer while scrolling

content/browser/renderer_host/touch_event_queue.cc

Index: content/browser/renderer_host/touch_event_queue.cc
diff --git a/content/browser/renderer_host/touch_event_queue.cc b/content/browser/renderer_host/touch_event_queue.cc
index cdabd1570dd1076498eb71af84e0a508c0d04c6b..eab2847a61286c663d3d3717d67572c08c3a1ab7 100644
--- a/content/browser/renderer_host/touch_event_queue.cc
+++ b/content/browser/renderer_host/touch_event_queue.cc
@@ -99,6 +99,7 @@ TouchEventQueue::~TouchEventQueue() {
 }
 
 void TouchEventQueue::QueueEvent(const TouchEventWithLatencyInfo& event) {
+  latest_event_ = event;
   if (touch_queue_.empty()) {
     // There is no touch event in the queue. Forward it to the renderer
     // immediately.
@@ -114,8 +115,10 @@ void TouchEventQueue::QueueEvent(const TouchEventWithLatencyInfo& event) {
   // also a touch-move, then the events can be coalesced into a single event.
   if (touch_queue_.size() > 1) {
     CoalescedWebTouchEvent* last_event = touch_queue_.back();
-    if (last_event->CoalesceEventIfPossible(event))
+    if (last_event->CoalesceEventIfPossible(event)) {
+      latest_event_ = last_event->coalesced_event();
       return;
+    }
   }
   touch_queue_.push_back(new CoalescedWebTouchEvent(event));
 }
@@ -124,6 +127,10 @@ void TouchEventQueue::ProcessTouchAck(InputEventAckState ack_result) {
   if (touch_queue_.empty())
     return;
 
+  // If scroll update is in progress, we should have cleared the touch
+  // event queue.
+  DCHECK(!render_widget_host_->is_scroll_update_in_progress());
+
   // Update the ACK status for each touch point in the ACKed event.
   const WebKit::WebTouchEvent& event =
       touch_queue_.front()->coalesced_event().event;
@@ -159,6 +166,19 @@ void TouchEventQueue::ProcessTouchAck(InputEventAckState ack_result) {
   }
 }
 
+void TouchEventQueue::OnGestureScrollStart() {
+  TouchEventWithLatencyInfo cancel_event = GetLatestEvent();
+  FlushQueue();
+  cancel_event.event.type = WebKit::WebInputEvent::TouchCancel;
+  for (size_t i = 0; i < cancel_event.event.touchesLength; i++)
+    cancel_event.event.touches[i].state = WebKit::WebTouchPoint::StateCancelled;
+  render_widget_host_->ForwardTouchEventImmediately(cancel_event);
+  // We only want to send the touch cancel to the renderer, but don't want
+  // it gets processed in view. So clear the touch event queue here and the
+  // ack for the cancel event will just be ignored.
+  Reset();
+}
+
 void TouchEventQueue::FlushQueue() {
   while (!touch_queue_.empty())
     PopTouchEventToView(INPUT_EVENT_ACK_STATE_NOT_CONSUMED);
@@ -174,7 +194,7 @@ size_t TouchEventQueue::GetQueueSize() const {
 }
 
 const TouchEventWithLatencyInfo& TouchEventQueue::GetLatestEvent() const {
-  return touch_queue_.back()->coalesced_event();

[sadrul, 2013/06/20 08:51:27]

When is touch_queue_ empty here?

[Yufeng Shen (Slow to review), 2013/06/20 17:56:45]

The PopTouchEventToView() below first pops the touch event in the queue, which
can make the queue empty. Then the popped touch event is sent to View, which can
result in a gesture event (e.g. ScrollUpdate). Then on receiving
GestureScrollUpdate, we want to make a cancel event from the latest event from
touch event queue, which could be empty.

+  return latest_event_;
 }
 
 void TouchEventQueue::PopTouchEventToView(InputEventAckState ack_result) {