Add UMA/Telemetry stats for touch event latency

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 "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/debug/trace_event.h"
@@ skipping 1784 matching lines @@
   aura::RootWindow* root = window_->GetRootWindow();
   // |root| is NULL during tests.
   if (!root)
     return;
 
   ui::EventResult result = (ack_result ==
       INPUT_EVENT_ACK_STATE_CONSUMED) ? ui::ER_HANDLED : ui::ER_UNHANDLED;
   for (ScopedVector<ui::TouchEvent>::iterator iter = events.begin(),
       end = events.end(); iter != end; ++iter) {
     (*iter)->latency()->AddLatencyNumber(
-        ui::INPUT_EVENT_LATENCY_ACKED_COMPONENT,
-        static_cast<int64>(ack_result),
-        0);
+        ui::INPUT_EVENT_LATENCY_ACKED_COMPONENT, 0, 0);
+    host_->ComputeTouchLatency(*((*iter)->latency()));

[sadrul, 2013/06/27 17:44:01]

Why is this called from here? Why not from
RWHI::OnInputEventAck/ProcessTouchAck?

[Yufeng Shen (Slow to review), 2013/06/27 19:01:03]

right, it is better to be in RWHI or touch_event_queue so we don't need to
do this for each view port.

Since we want to add the ACKED_COMPONENT for each uncoalesced (Web/UI)touch
event so I feel it is proper to do it in TouchEventQueue::PopTouchEventToView()
where we extract each individual touch event out and before calling view's
ProcessAckedTouchEvent.
So move the code to TouchEventQueue::PopTouchEventToView(). 

     root->ProcessedTouchEvent((*iter), window_, result);
   }
 }
 
 SmoothScrollGesture* RenderWidgetHostViewAura::CreateSmoothScrollGesture(
     bool scroll_down,
     int pixels_to_scroll,
     int mouse_event_x,
     int mouse_event_y) {
   return new TouchSmoothScrollGestureAura(scroll_down,
@@ skipping 1194 matching lines @@
     RenderWidgetHost* widget) {
   return new RenderWidgetHostViewAura(widget);
 }
 
 // static
 void RenderWidgetHostViewPort::GetDefaultScreenInfo(WebScreenInfo* results) {
   GetScreenInfoForWindow(results, NULL);
 }
 
 }  // namespace content