Notify Blink about start of gesture scroll through a queued event.

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 265f5f11b6d9b12c863ab100b0c2639d4bfe9ab3..a86ca799a1d5b659d9266bc145462efb6e4709de 100644
--- a/content/browser/renderer_host/input/touch_event_queue.cc
+++ b/content/browser/renderer_host/input/touch_event_queue.cc
@@ -459,6 +459,9 @@ TouchEventQueue::~TouchEventQueue() {
 
 void TouchEventQueue::QueueEvent(const TouchEventWithLatencyInfo& event) {
   TRACE_EVENT0("input", "TouchEventQueue::QueueEvent");
+  LOG(ERROR) << "======= mDebug " << __FUNCTION__
+             << " t=" << WebInputEventTraits::GetName(event.event.type)
+             << " |q|=" << touch_queue_.size();
 
   // If the queueing of |event| was triggered by an ack dispatch, defer
   // processing the event until the dispatch has finished.
@@ -492,6 +495,24 @@ void TouchEventQueue::QueueEvent(const TouchEventWithLatencyInfo& event) {
   touch_queue_.push_back(new CoalescedWebTouchEvent(event, false));
 }
 
+void TouchEventQueue::PrependTouchScrollNotification() {
+  TRACE_EVENT0("input", "TouchEventQueue::PrependTouchScrollNotification");
+  LOG(ERROR) << "======= mDebug " << __FUNCTION__
+             << " |q|=" << touch_queue_.size();
+
+  TouchEventWithLatencyInfo touch;
+  touch.event.type = WebInputEvent::TouchScrollStarted;
+  touch.event.uniqueTouchEventId = 12345;
+  touch.event.touchesLength = 0;
+
+  // Skip the head of the queue to avoid messing up with in-flight event's ack.
+  auto it = touch_queue_.begin();
+  if (it != touch_queue_.end())
+      ++it;
+  touch_queue_.insert(it, new CoalescedWebTouchEvent(touch, false));
+}
+
+
 void TouchEventQueue::ProcessTouchAck(InputEventAckState ack_result,
                                       const LatencyInfo& latency_info,
                                       const uint32_t unique_touch_event_id) {
@@ -746,6 +767,10 @@ void TouchEventQueue::AckTouchEventToClient(
 scoped_ptr<CoalescedWebTouchEvent> TouchEventQueue::PopTouchEvent() {
   DCHECK(!touch_queue_.empty());
   scoped_ptr<CoalescedWebTouchEvent> event(touch_queue_.front());
+  LOG(ERROR) << "======= mDebug " << __FUNCTION__
+             << " t=" << WebInputEventTraits::GetName(
+                             event->coalesced_event().event.type)
+             << " |q|=" << touch_queue_.size();
   touch_queue_.pop_front();
   return event;
 }
@@ -831,6 +856,9 @@ TouchEventQueue::FilterBeforeForwarding(const WebTouchEvent& event) {
     return ACK_WITH_NO_CONSUMER_EXISTS;
   }
 
+  if (event.type == WebInputEvent::TouchScrollStarted)
+    return FORWARD_TO_RENDERER;

[tdresser, 2016/03/16 14:56:31]

Are we returning before this for some TouchScrollStarted events?

[mustaq, 2016/03/16 15:15:40]

That's a possibility of course, but not in the case I am looking at now. See
below.

+
   if (event.type == WebInputEvent::TouchStart) {
     return (has_handlers_ || has_handler_for_current_sequence_)
                ? FORWARD_TO_RENDERER