Only store leading 13 bits of password hash.

chrome/browser/signin/local_auth.h

 // Copyright 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.
 //
 // The local-auth module allows for user authentication in the case when
 // on-line authentication is not possible (e.g. there is no network
 // connection).
 
 #ifndef CHROME_BROWSER_SIGNIN_LOCAL_AUTH_H_
 #define CHROME_BROWSER_SIGNIN_LOCAL_AUTH_H_
 
 #include <string>
 
 class Profile;
 
 namespace user_prefs {
 class PrefRegistrySyncable;
 }
 
 namespace chrome {
 
 void RegisterLocalAuthPrefs(user_prefs::PrefRegistrySyncable* registry);
 
 void SetLocalAuthCredentials(size_t profile_info_index,
                              const std::string& password);
 
+// For use by tests only to ensure backward compatibility.
+void SetLocalAuthCredentialsWithEncoding(size_t profile_info_index,
+                                         const std::string& password,
+                                         char encoding_version);
+
 void SetLocalAuthCredentials(const Profile* profile,
                              const std::string& password);
 
 bool ValidateLocalAuthCredentials(size_t profile_info_index,
                                   const std::string& password);
 
 bool ValidateLocalAuthCredentials(const Profile* profile,
                                   const std::string& password);
 
+// Return only the first |len_bits| bits of the string |str|.
+std::string TruncateStringByBits(const std::string& str, const size_t len_bits);
+
 }  // namespace chrome
 
 #endif  // CHROME_BROWSER_SIGNIN_LOCAL_AUTH_H_