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

base/json/json_string_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_STRING_VALUE_SERIALIZER_H_
 #define BASE_JSON_JSON_STRING_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 JSONStringValueSerializer : public base::ValueSerializer {
  public:
@@ skipping 51 matching lines @@
   bool initialized_with_const_string_;
   bool pretty_print_;  // If true, serialization will span multiple lines.
   // If true, deserialization will allow trailing commas.
   bool allow_trailing_comma_;
 
   DISALLOW_COPY_AND_ASSIGN(JSONStringValueSerializer);
 };
 
 #endif  // BASE_JSON_JSON_STRING_VALUE_SERIALIZER_H_