Remove #pragma once. Just from base/ for now.

base/metrics/stats_counters.h

 // 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.
 
 #ifndef BASE_METRICS_STATS_COUNTERS_H_
 #define BASE_METRICS_STATS_COUNTERS_H_
-#pragma once
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/compiler_specific.h"
 #include "base/metrics/stats_table.h"
 #include "base/time.h"
 
 namespace base {
 
@@ skipping 171 matching lines @@
     timer_.Stop();
   }
 
  private:
   T& timer_;
 };
 
 }  // namespace base
 
 #endif  // BASE_METRICS_STATS_COUNTERS_H_