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

content/browser/renderer_host/render_widget_host_view_aura.cc

 // Copyright (c) 2012 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #include "content/browser/renderer_host/render_widget_host_view_aura.h"
 
 #include <set>
 #include <utility>
 
 #include "base/auto_reset.h"
@@ skipping 1127 matching lines @@
 
 void RenderWidgetHostViewAura::ProcessAckedTouchEvent(
     const TouchEventWithLatencyInfo& touch,
     InputEventAckState ack_result) {
   ScopedVector<ui::TouchEvent> events;
   aura::WindowTreeHost* host = window_->GetHost();
   // |host| is NULL during tests.
   if (!host)
     return;
 
+  // The TouchScrollStarted event is generated & consumed downstream from the
+  // TouchEventQueue. So we don't expect an ACK up here.
+  DCHECK(touch.event.type != blink::WebInputEvent::TouchScrollStarted);
+
   ui::EventResult result = (ack_result == INPUT_EVENT_ACK_STATE_CONSUMED)
                                ? ui::ER_HANDLED
                                : ui::ER_UNHANDLED;
 
   blink::WebTouchPoint::State required_state;
   switch (touch.event.type) {
     case blink::WebInputEvent::TouchStart:
       required_state = blink::WebTouchPoint::StatePressed;
       break;
     case blink::WebInputEvent::TouchEnd:
@@ skipping 1775 matching lines @@
 
 ////////////////////////////////////////////////////////////////////////////////
 // RenderWidgetHostViewBase, public:
 
 // static
 void RenderWidgetHostViewBase::GetDefaultScreenInfo(WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }
 
 }  // namespace content