More header cleanup:

chrome/browser/sessions/session_service.cc

 // Copyright (c) 2010 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 "build/build_config.h"
 
 #include "chrome/browser/sessions/session_service.h"
 
 #include <limits>
 
 #include "base/callback.h"
 #include "base/file_util.h"
+#include "base/histogram.h"
 #include "base/message_loop.h"
 #include "base/pickle.h"
 #include "base/scoped_vector.h"
 #include "base/thread.h"
 #include "chrome/browser/browser_init.h"
 #include "chrome/browser/browser_list.h"
 #include "chrome/browser/browser_process.h"
 #include "chrome/browser/browser_window.h"
 #include "chrome/browser/defaults.h"
 #include "chrome/browser/profile.h"
@@ skipping 1317 matching lines @@
       UMA_HISTOGRAM_CUSTOM_TIMES("SessionRestore.LongSavePeriod",
           delta,
           base::TimeDelta::FromMinutes(10),
           base::TimeDelta::FromHours(8),
           50);
     }
   }
 
   last_save_time_ = base::TimeTicks::Now();
 }