Add UMA/Telemetry stats for touch event latency

content/browser/renderer_host/touch_event_queue.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/touch_event_queue.h"
 
 #include "base/debug/trace_event.h"
 #include "base/stl_util.h"
 #include "content/browser/renderer_host/render_widget_host_impl.h"
 #include "content/public/browser/render_widget_host_view.h"
@@ skipping 169 matching lines @@
 void TouchEventQueue::PopTouchEventToView(InputEventAckState ack_result) {
   if (touch_queue_.empty())
     return;
   scoped_ptr<CoalescedWebTouchEvent> acked_event(touch_queue_.front());
   touch_queue_.pop_front();
 
   // Note that acking the touch-event may result in multiple gestures being sent
   // to the renderer.
   RenderWidgetHostViewPort* view = RenderWidgetHostViewPort::FromRWHV(
       render_widget_host_->GetView());
   for (WebTouchEventWithLatencyList::const_iterator iter = acked_event->begin(),

[sadrul, 2013/06/27 22:40:12]

You probably can just use an iterator here instead of a const_iterator, and then
not have to do the const_cast below.

[Yufeng Shen (Slow to review), 2013/06/27 23:44:07]

begin() only returns const_iterator so we have to do the const_cast anyway or we
add a non-const version of begin(). 

        end = acked_event->end();
        iter != end; ++iter) {
+    ui::LatencyInfo* latency = const_cast<ui::LatencyInfo*>(&(iter->latency));
+    latency->AddLatencyNumber(
+        ui::INPUT_EVENT_LATENCY_ACKED_COMPONENT, 0, 0);
+    render_widget_host_->ComputeTouchLatency(*latency);
     view->ProcessAckedTouchEvent((*iter), ack_result);
   }
 }
 
 bool TouchEventQueue::ShouldForwardToRenderer(
     const WebKit::WebTouchEvent& event) const {
   // Touch press events should always be forwarded to the renderer.
   if (event.type == WebKit::WebInputEvent::TouchStart)
     return true;
 
@@ skipping 11 matching lines @@
       // If the ACK status of a point is unknown, then the event should be
       // forwarded to the renderer.
       return true;
     }
   }
 
   return false;
 }
 
 }  // namespace content