This CL replaces std::string user_id in ash/* with AccountId.

ash/test/test_session_state_delegate.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.
 
 #ifndef ASH_TEST_TEST_SESSION_STATE_DELEGATE_H_
 #define ASH_TEST_TEST_SESSION_STATE_DELEGATE_H_
 
 #include <vector>
 
 #include "ash/session/session_state_delegate.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "base/memory/scoped_ptr.h"
 #include "ui/gfx/image/image_skia.h"
 
+class AccountId;
+
 namespace ash {
 namespace test {
 
 class MockUserInfo;
 
 class TestSessionStateDelegate : public SessionStateDelegate {
  public:
   TestSessionStateDelegate();
   ~TestSessionStateDelegate() override;
 
   void set_logged_in_users(int users) { logged_in_users_ = users; }
   void set_session_state(SessionState session_state) {
     session_state_ = session_state;
   }
-  void AddUser(const std::string& user_id);
+  void AddUser(const AccountId& account_id);
   const user_manager::UserInfo* GetActiveUserInfo() const;
 
   // SessionStateDelegate:
   int GetMaximumNumberOfLoggedInUsers() const override;
   int NumberOfLoggedInUsers() const override;
   bool IsActiveUserSessionStarted() const override;
   bool CanLockScreen() const override;
   bool IsScreenLocked() const override;
   bool ShouldLockScreenBeforeSuspending() const override;
   void LockScreen() override;
   void UnlockScreen() override;
   bool IsUserSessionBlocked() const override;
   SessionState GetSessionState() const override;
   const user_manager::UserInfo* GetUserInfo(
       ash::UserIndex index) const override;
   bool ShouldShowAvatar(aura::Window* window) const override;
   gfx::ImageSkia GetAvatarImageForWindow(aura::Window* window) const override;
-  void SwitchActiveUser(const std::string& user_id) override;
+  void SwitchActiveUser(const AccountId& account_id) override;
   void CycleActiveUser(CycleUser cycle_user) override;
   bool IsMultiProfileAllowedByPrimaryUserPolicy() const override;
   void AddSessionStateObserver(ash::SessionStateObserver* observer) override;
   void RemoveSessionStateObserver(ash::SessionStateObserver* observer) override;
 
   // TODO(oshima): Use state machine instead of using boolean variables.
 
   // Updates the internal state that indicates whether a session is in progress
   // and there is an active user. If |has_active_user| is |false|,
   // |active_user_session_started_| is reset to |false| as well (see below for
@@ skipping 52 matching lines @@
   // before the profile and browser UI are available.
   SessionState session_state_;
 
   DISALLOW_COPY_AND_ASSIGN(TestSessionStateDelegate);
 };
 
 }  // namespace test
 }  // namespace ash
 
 #endif  // ASH_TEST_TEST_SESSION_STATE_DELEGATE_H_