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

content/browser/renderer_host/input/touch_event_queue.h

Index: content/browser/renderer_host/input/touch_event_queue.h
diff --git a/content/browser/renderer_host/input/touch_event_queue.h b/content/browser/renderer_host/input/touch_event_queue.h
index 8a19586c618845acb6440c48b2dd0f2409e07e19..b5f6b458d5a72477a73ec82cb5fa99273acf05af 100644
--- a/content/browser/renderer_host/input/touch_event_queue.h
+++ b/content/browser/renderer_host/input/touch_event_queue.h
@@ -9,6 +9,7 @@
 #include <stdint.h>
 
 #include <deque>
+#include <list>
 #include <map>
 
 #include "base/macros.h"
@@ -70,6 +71,9 @@ class CONTENT_EXPORT TouchEventQueue {
   // the renderer (e.g. when there are no other queued touch event).
   void QueueEvent(const TouchEventWithLatencyInfo& event);
 
+  // Adds a TouchScrollStarted event to the front of the queue.

[tdresser, 2016/03/30 19:19:01]

This comment is a bit misleading, as it's often placed second in the queue.

[mustaq, 2016/03/30 20:21:05]

It is better? Or you want to see something like "1st or 2nd place"?

+  void PrependTouchScrollNotification();
+
   // Notifies the queue that a touch-event has been processed by the renderer.
   // At this point, if the ack is for async touchmove, remove the uncancelable
   // touchmove from the front of the queue and decide if it should dispatch the
@@ -109,8 +113,6 @@ class CONTENT_EXPORT TouchEventQueue {
   // Whether ack timeout behavior is supported and enabled for the current site.
   bool IsAckTimeoutEnabled() const;
 
-  bool IsForwardingTouches();
-
   bool empty() const WARN_UNUSED_RESULT {
     return touch_queue_.empty();
   }
@@ -155,15 +157,12 @@ class CONTENT_EXPORT TouchEventQueue {
   void PopTouchEventToClient(InputEventAckState ack_result,
                              const ui::LatencyInfo& renderer_latency_info);
 
-  // Ack all coalesced events in |acked_event| to the client with |ack_result|,
-  // updating the acked events with |optional_latency_info| if it exists.
+  // Ack all coalesced events at the head of the queue to the client with
+  // |ack_result|, updating the acked events with |optional_latency_info| if it
+  // exists, and popping the head of the queue.
   void AckTouchEventToClient(InputEventAckState ack_result,
-                             scoped_ptr<CoalescedWebTouchEvent> acked_event,
                              const ui::LatencyInfo* optional_latency_info);
 
-  // Safely pop the head of the queue.
-  scoped_ptr<CoalescedWebTouchEvent> PopTouchEvent();
-
   // Dispatch |touch| to the client. Before dispatching, updates pointer
   // states in touchmove events for pointers that have not changed position.
   void SendTouchEventImmediately(TouchEventWithLatencyInfo* touch);
@@ -184,7 +183,7 @@ class CONTENT_EXPORT TouchEventQueue {
   // Handles touch event forwarding and ack'ed event dispatch.
   TouchEventQueueClient* client_;
 
-  typedef std::deque<CoalescedWebTouchEvent*> TouchQueue;
+  typedef std::list<CoalescedWebTouchEvent*> TouchQueue;
   TouchQueue touch_queue_;
 
   // Position of the first touch in the most recent sequence forwarded to the