Add standard policy provider tests for PReg policy reading.

chrome/browser/policy/preg_parser_win.h

 // Copyright (c) 2013 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.
 
 // This file provides a parser for PReg files which are used for storing group
 // policy settings in the file system. The file format is documented here:
 //
 // http://msdn.microsoft.com/en-us/library/windows/desktop/aa374407(v=vs.85).aspx
 
 #ifndef CHROME_BROWSER_POLICY_PREG_PARSER_WIN_H_
 #define CHROME_BROWSER_POLICY_PREG_PARSER_WIN_H_
 
 #include <vector>
 
 #include "base/memory/scoped_ptr.h"
 #include "base/string16.h"
 
 namespace base {
 class DictionaryValue;
 class FilePath;
 }
 
 namespace policy {
 namespace preg_parser {
 
+// The magic header in PReg files: ASCII "PReg" + version (0x0001).
+extern const char kPRegFileHeader[8];
+
 // Reads the PReg file at |file_path| and writes the registry data to |dict|.
 // |root| specifies the registry subtree the caller is interested in,
 // everything else gets ignored.
 bool ReadFile(const base::FilePath& file_path,
               const string16& root,
               base::DictionaryValue* dict);
 
 }  // namespace preg_parser
 }  // namespace policy
 
 #endif  // CHROME_BROWSER_POLICY_PREG_PARSER_WIN_H_