Use lock-free lazy initialization for static histogram references

chrome/browser/metrics/thread_watcher.cc

 // Copyright (c) 2011 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 "base/threading/thread_restrictions.h"
 #include "build/build_config.h"
 #include "chrome/browser/metrics/metrics_service.h"
 #include "chrome/browser/metrics/thread_watcher.h"
 #include "content/common/notification_service.h"
 
@@ skipping 10 matching lines @@
                              const base::TimeDelta& sleep_time,
                              const base::TimeDelta& unresponsive_time)
     : thread_id_(thread_id),
       thread_name_(thread_name),
       sleep_time_(sleep_time),
       unresponsive_time_(unresponsive_time),
       ping_time_(base::TimeTicks::Now()),
       ping_sequence_number_(0),
       active_(false),
       ping_count_(kPingCount),
+      histogram_(NULL),
       ALLOW_THIS_IN_INITIALIZER_LIST(method_factory_(this)) {
   Initialize();
 }
 
 ThreadWatcher::~ThreadWatcher() {}
 
 // static
 void ThreadWatcher::StartWatching(const BrowserThread::ID& thread_id,
                                   const std::string& thread_name,
                                   const base::TimeDelta& sleep_time,
@@ skipping 379 matching lines @@
   watchdog_thread_ = NULL;
 }
 
 void WatchDogThread::CleanUpAfterMessageLoopDestruction() {
 #if defined(OS_WIN)
   // Closes the COM library on the current thread. CoInitialize must
   // be balanced by a corresponding call to CoUninitialize.
   CoUninitialize();
 #endif
 }