Fix LatencyInfo compile error for ipc fuzzer

ui/events/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 UI_EVENTS_LATENCY_INFO_H_
 #define UI_EVENTS_LATENCY_INFO_H_
 
 #include <string>
 #include <utility>
 #include <vector>
 
 #include "base/basictypes.h"
 #include "base/containers/small_map.h"
 #include "base/gtest_prod_util.h"
 #include "base/memory/scoped_ptr.h"
 #include "base/time/time.h"
 #include "base/trace_event/trace_event.h"
 #include "ipc/ipc_param_traits.h"
 #include "ui/events/events_base_export.h"
 
+namespace ipc_fuzzer {

[inferno, 2015/08/05 15:40:01]

We never sprinkle ipc fuzzer code in regular builds, so please remove changes in
this file.

[Yufeng Shen (Slow to review), 2015/08/05 16:08:24]

I copied from here 
https://code.google.com/p/chromium/codesearch#search/&q=%22friend%20struct%20...

guess it is better to clean those up ?

+template <class T>
+struct FuzzTraits;
+}  // namespace ipc_fuzzer
+
 namespace ui {
 
 enum LatencyComponentType {
   // ---------------------------BEGIN COMPONENT-------------------------------
   // BEGIN COMPONENT is when we show the latency begin in chrome://tracing.
   // Timestamp when the input event is sent from RenderWidgetHost to renderer.
   INPUT_EVENT_LATENCY_BEGIN_RWH_COMPONENT,
   // In threaded scrolling, main thread scroll listener update is async to
   // scroll processing in impl thread. This is the timestamp when we consider
   // the main thread scroll listener update is begun.
@@ skipping 174 matching lines @@
   uint32 input_coordinates_size_;
   InputCoordinate input_coordinates_[kMaxInputCoordinates];
 
   // The unique id for matching the ASYNC_BEGIN/END trace event.
   int64 trace_id_;
   // Whether a terminal component has been added.
   bool terminated_;
 
   FRIEND_TEST_ALL_PREFIXES(LatencyInfoParamTraitsTest, Basic);
   friend struct IPC::ParamTraits<ui::LatencyInfo>;
+  friend struct ipc_fuzzer::FuzzTraits<ui::LatencyInfo>;
 };
 
 }  // namespace ui
 
 #endif  // UI_EVENTS_LATENCY_INFO_H_