Add UMA/Telemetry stats for touch event latency

content/browser/renderer_host/touch_event_queue.cc

Index: content/browser/renderer_host/touch_event_queue.cc
diff --git a/content/browser/renderer_host/touch_event_queue.cc b/content/browser/renderer_host/touch_event_queue.cc
index cdabd1570dd1076498eb71af84e0a508c0d04c6b..68788117a7c41f329e893436da234d33cefadacc 100644
--- a/content/browser/renderer_host/touch_event_queue.cc
+++ b/content/browser/renderer_host/touch_event_queue.cc
@@ -190,6 +190,10 @@ void TouchEventQueue::PopTouchEventToView(InputEventAckState ack_result) {
   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);
   }
 }