Reland of This CL replaces e-mail with AccountId on user selection screen.

components/user_manager/user.h

 // Copyright 2014 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 COMPONENTS_USER_MANAGER_USER_H_
 #define COMPONENTS_USER_MANAGER_USER_H_
 
 #include <string>
 #include <vector>
 
@@ skipping 79 matching lines @@
   base::string16 display_name() const { return display_name_; }
 
   // If the user has to use SAML to log in.
   bool using_saml() const { return using_saml_; }
 
   // UserInfo
   std::string GetEmail() const override;
   base::string16 GetDisplayName() const override;
   base::string16 GetGivenName() const override;
   const gfx::ImageSkia& GetImage() const override;
-  AccountId GetAccountId() const override;
+  const AccountId& GetAccountId() const override;
 
   // Allows managing child status of the user. Used for RegularUser.
   virtual void SetIsChild(bool is_child);
 
   // Returns true if user has gaia account. True for users of types
   // USER_TYPE_REGULAR and USER_TYPE_CHILD.
   virtual bool HasGaiaAccount() const;
 
   // Returns true if user is supervised.
   virtual bool IsSupervised() const;
@@ skipping 187 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(User);
 };
 
 // List of known users.
 using UserList = std::vector<User*>;
 
 }  // namespace user_manager
 
 #endif  // COMPONENTS_USER_MANAGER_USER_H_