Use lock-free lazy initialization for static histogram references

chrome/browser/sessions/session_restore.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 "chrome/browser/sessions/session_restore.h"
 
 #include <algorithm>
 #include <list>
 #include <set>
 #include <vector>
@@ skipping 282 matching lines @@
           UMA_HISTOGRAM_CUSTOM_TIMES(
               "SessionRestore.FirstTabPainted",
               time_to_paint,
               base::TimeDelta::FromMilliseconds(10),
               base::TimeDelta::FromSeconds(100),
               100);
           // Record a time for the number of tabs, to help track down
           // contention.
           std::string time_for_count =
               StringPrintf("SessionRestore.FirstTabPainted_%d", tab_count_);
-          scoped_refptr<base::Histogram> counter_for_count =
+          base::Histogram* counter_for_count =
               base::Histogram::FactoryTimeGet(
                   time_for_count,
                   base::TimeDelta::FromMilliseconds(10),
                   base::TimeDelta::FromSeconds(100),
                   100,
                   base::Histogram::kUmaTargetedHistogramFlag);
           counter_for_count->AddTime(time_to_paint);
         } else if (render_widget_hosts_loading_.find(render_widget_host) ==
             render_widget_hosts_loading_.end()) {
           // If this is a host for a tab we're not loading some other tab
@@ skipping 67 matching lines @@
         base::TimeTicks::Now() - restore_started_;
     UMA_HISTOGRAM_CUSTOM_TIMES(
         "SessionRestore.AllTabsLoaded",
         time_to_load,
         base::TimeDelta::FromMilliseconds(10),
         base::TimeDelta::FromSeconds(100),
         100);
     // Record a time for the number of tabs, to help track down contention.
     std::string time_for_count =
         StringPrintf("SessionRestore.AllTabsLoaded_%d", tab_count_);
-    scoped_refptr<base::Histogram> counter_for_count =
+    base::Histogram* counter_for_count =
         base::Histogram::FactoryTimeGet(
             time_for_count,
             base::TimeDelta::FromMilliseconds(10),
             base::TimeDelta::FromSeconds(100),
             100,
             base::Histogram::kUmaTargetedHistogramFlag);
     counter_for_count->AddTime(time_to_load);
   }
 }
 
@@ skipping 437 matching lines @@
 Browser* SessionRestore::RestoreSessionSynchronously(
     Profile* profile,
     const std::vector<GURL>& urls_to_open) {
   return Restore(profile, NULL, true, false, true, urls_to_open);
 }
 
 // static
 bool SessionRestore::IsRestoring() {
   return restoring;
 }