Stop sending an async touchmove for the app slop region

content/browser/renderer_host/input/touch_event_queue.cc

Index: content/browser/renderer_host/input/touch_event_queue.cc
diff --git a/content/browser/renderer_host/input/touch_event_queue.cc b/content/browser/renderer_host/input/touch_event_queue.cc
index c22cbc51f38e296809ac32f8f160864d6c63392b..0b183112be0caebe97c5c1d4c631768d3f3f81ae 100644
--- a/content/browser/renderer_host/input/touch_event_queue.cc
+++ b/content/browser/renderer_host/input/touch_event_queue.cc
@@ -364,6 +364,7 @@ TouchEventQueue::TouchEventQueue(TouchEventQueueClient* client,
     : client_(client),
       dispatching_touch_ack_(NULL),
       dispatching_touch_(false),
+      processing_touch_ack_(false),
       has_handlers_(true),
       drop_remaining_touches_in_sequence_(false),
       touchmove_slop_suppressor_(new TouchMoveSlopSuppressor),
@@ -420,6 +421,7 @@ void TouchEventQueue::QueueEvent(const TouchEventWithLatencyInfo& event) {
 void TouchEventQueue::ProcessTouchAck(InputEventAckState ack_result,
                                       const LatencyInfo& latency_info) {
   TRACE_EVENT0("input", "TouchEventQueue::ProcessTouchAck");
+  base::AutoReset<bool> processing_touch_ack(&processing_touch_ack_, true);
 
   DCHECK(!dispatching_touch_ack_);
   dispatching_touch_ = false;
@@ -471,15 +473,20 @@ void TouchEventQueue::ForwardNextEventToRenderer() {
     // application be sent touches at key points in the gesture stream,
     // e.g., when the application slop region is exceeded or touchmove
     // coalescing fails because of different modifiers.
-    const bool send_touchmove_now =
-        size() > 1 ||
-        (touch.event.timeStampSeconds >=
-         last_sent_touch_timestamp_sec_ + kAsyncTouchMoveIntervalSec) ||
-        (needs_async_touchmove_for_outer_slop_region_ &&
-         OutsideApplicationSlopRegion(touch.event,
-                                      touch_sequence_start_position_)) ||
-        (pending_async_touchmove_ &&
-         !pending_async_touchmove_->CanCoalesceWith(touch));
+    bool send_touchmove_now = size() > 1;
+    send_touchmove_now |= pending_async_touchmove_ &&
+                          !pending_async_touchmove_->CanCoalesceWith(touch);
+    // Avoid async touch dispatch immediately after receipt of a touch ack. This
+    // reduces the likelihood of the async touch contending with gestures
+    // (and gesture side effects) triggered by the touch ack.
+    if (!processing_touch_ack_) {
+      send_touchmove_now |=
+          touch.event.timeStampSeconds >=
+          last_sent_touch_timestamp_sec_ + kAsyncTouchMoveIntervalSec;
+      send_touchmove_now |= needs_async_touchmove_for_outer_slop_region_ &&
+                            OutsideApplicationSlopRegion(
+                                touch.event, touch_sequence_start_position_);
+    }
 
     if (!send_touchmove_now) {
       if (!pending_async_touchmove_) {