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

base/json/json_file_value_serializer.h

 // Copyright (c) 2012 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_JSON_JSON_FILE_VALUE_SERIALIZER_H_
 #define BASE_JSON_JSON_FILE_VALUE_SERIALIZER_H_
-#pragma once
 
 #include <string>
 
 #include "base/base_export.h"
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "base/values.h"
 
 class BASE_EXPORT JSONFileValueSerializer : public base::ValueSerializer {
  public:
@@ skipping 62 matching lines @@
 
   // A wrapper for file_util::ReadFileToString which returns a non-zero
   // JsonFileError if there were file errors.
   int ReadFileToString(std::string* json_string);
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(JSONFileValueSerializer);
 };
 
 #endif  // BASE_JSON_JSON_FILE_VALUE_SERIALIZER_H_