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

chrome/browser/ui/ash/session_state_delegate_views.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 CHROME_BROWSER_UI_ASH_SESSION_STATE_DELEGATE_VIEWS_H_
 #define CHROME_BROWSER_UI_ASH_SESSION_STATE_DELEGATE_VIEWS_H_
 
 #include "ash/session/session_state_delegate.h"
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
@@ skipping 17 matching lines @@
   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;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(SessionStateDelegate);
 };
 
 #endif  // CHROME_BROWSER_UI_ASH_SESSION_STATE_DELEGATE_VIEWS_H_