Factor out latency tracking from RenderWidgetHostImpl

content/browser/renderer_host/event_with_latency_info.h

 // Copyright 2013 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.
 
 #ifndef CONTENT_BROWSER_RENDERER_HOST_EVENT_WITH_LATENCY_INFO_H_
 #define CONTENT_BROWSER_RENDERER_HOST_EVENT_WITH_LATENCY_INFO_H_
 
 #include "ui/events/latency_info.h"
 
 #include "content/common/input/web_input_event_traits.h"
 
 namespace blink {
 class WebGestureEvent;
 class WebMouseEvent;
 class WebMouseWheelEvent;
 class WebTouchEvent;
 }
 
 namespace content {
 
 template <typename T>
 class EventWithLatencyInfo {
  public:
   T event;
-  ui::LatencyInfo latency;
+  mutable ui::LatencyInfo latency;
+
+  explicit EventWithLatencyInfo(const T& e) : event(e) {}
 
   EventWithLatencyInfo(const T& e, const ui::LatencyInfo& l)
       : event(e), latency(l) {}
 
   EventWithLatencyInfo() {}
 
   bool CanCoalesceWith(const EventWithLatencyInfo& other)
       const WARN_UNUSED_RESULT {
     return WebInputEventTraits::CanCoalesce(other.event, event);
   }
@@ skipping 14 matching lines @@
 typedef EventWithLatencyInfo<blink::WebMouseWheelEvent>
     MouseWheelEventWithLatencyInfo;
 typedef EventWithLatencyInfo<blink::WebMouseEvent>
     MouseEventWithLatencyInfo;
 typedef EventWithLatencyInfo<blink::WebTouchEvent>
     TouchEventWithLatencyInfo;
 
 }  // namespace content
 
 #endif  // CONTENT_BROWSER_RENDERER_HOST_EVENT_WITH_LATENCY_INFO_H_