Reset user data directory and disk cache directory after downgrade.

chrome/browser/policy/policy_path_parser_mac.mm

 // 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.
 
 #include "chrome/browser/policy/policy_path_parser.h"
 
 #import <Cocoa/Cocoa.h>
 #include <stddef.h>
 #import <SystemConfiguration/SCDynamicStore.h>
 #import <SystemConfiguration/SCDynamicStoreCopySpecific.h>
@@ skipping 96 matching lines @@
   NSUserDefaults* defaults = [NSUserDefaults standardUserDefaults];
   NSString* value = [defaults stringForKey:key];
   if (value && [defaults objectIsForcedForKey:key]) {
     std::string string_value = base::SysNSStringToUTF8(value);
     // Now replace any vars the user might have used.
     string_value = policy::path_parser::ExpandPathVariables(string_value);
     *user_data_dir = base::FilePath(string_value);
   }
 }
 
+void CheckDiskCacheDirPolicy(base::FilePath* user_data_dir) {
+  // This function is not implemented in Mac because it's only used by the
+  // feature in Windows.
+  NOTREACHED();
+}
+
 }  // namespace path_parser
 
 }  // namespace policy