ChromeOS cryptohome should be able to use gaia id as user identifier.

chrome/browser/chromeos/settings/device_settings_test_helper.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 CHROME_BROWSER_CHROMEOS_SETTINGS_DEVICE_SETTINGS_TEST_HELPER_H_
 #define CHROME_BROWSER_CHROMEOS_SETTINGS_DEVICE_SETTINGS_TEST_HELPER_H_
 
 #include <map>
 #include <string>
 #include <vector>
@@ skipping 71 matching lines @@
 
   // SessionManagerClient:
   void Init(dbus::Bus* bus) override;
   void SetStubDelegate(SessionManagerClient::StubDelegate* delegate) override;
   void AddObserver(Observer* observer) override;
   void RemoveObserver(Observer* observer) override;
   bool HasObserver(const Observer* observer) const override;
   bool IsScreenLocked() const override;
   void EmitLoginPromptVisible() override;
   void RestartJob(const std::vector<std::string>& argv) override;
-  void StartSession(const std::string& user_email) override;
+  void StartSession(const cryptohome::Identification& cryptohome_id) override;
   void StopSession() override;
   void NotifySupervisedUserCreationStarted() override;
   void NotifySupervisedUserCreationFinished() override;
   void StartDeviceWipe() override;
   void RequestLockScreen() override;
   void NotifyLockScreenShown() override;
   void NotifyLockScreenDismissed() override;
   void RetrieveActiveSessions(const ActiveSessionsCallback& callback) override;
   void RetrieveDevicePolicy(const RetrievePolicyCallback& callback) override;
-  void RetrievePolicyForUser(const std::string& username,
+  void RetrievePolicyForUser(const cryptohome::Identification& cryptohome_id,
                              const RetrievePolicyCallback& callback) override;
   std::string BlockingRetrievePolicyForUser(
-      const std::string& username) override;
+      const cryptohome::Identification& cryptohome_id) override;
   void RetrieveDeviceLocalAccountPolicy(
       const std::string& account_id,
       const RetrievePolicyCallback& callback) override;
   void StoreDevicePolicy(const std::string& policy_blob,
                          const StorePolicyCallback& callback) override;
-  void StorePolicyForUser(const std::string& username,
+  void StorePolicyForUser(const cryptohome::Identification& cryptohome_id,
                           const std::string& policy_blob,
                           const StorePolicyCallback& callback) override;
   void StoreDeviceLocalAccountPolicy(
       const std::string& account_id,
       const std::string& policy_blob,
       const StorePolicyCallback& callback) override;
-  void SetFlagsForUser(const std::string& account_id,
+  void SetFlagsForUser(const cryptohome::Identification& cryptohome_id,
                        const std::vector<std::string>& flags) override;
   void GetServerBackedStateKeys(const StateKeysCallback& callback) override;
 
   void CheckArcAvailability(const ArcCallback& callback) override;
   void StartArcInstance(const std::string& socket_path,
                         const ArcCallback& callback) override;
   void StopArcInstance(const ArcCallback& callback) override;
 
  private:
   struct PolicyState {
@@ skipping 65 matching lines @@
 
   scoped_ptr<DBusThreadManagerSetter> dbus_setter_;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(DeviceSettingsTestBase);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_SETTINGS_DEVICE_SETTINGS_TEST_HELPER_H_