Implement oauth token external handler checking.

components/user_manager/user.h

Index: components/user_manager/user.h
diff --git a/components/user_manager/user.h b/components/user_manager/user.h
index a413cce1806eaa8b14a9ef1fda2399b3924a5ed1..39b718238b4116590bdf80c5af612575af07511f 100644
--- a/components/user_manager/user.h
+++ b/components/user_manager/user.h
@@ -10,6 +10,7 @@
 
 #include "base/basictypes.h"
 #include "base/strings/string16.h"
+#include "components/user_manager/user_id.h"
 #include "components/user_manager/user_image/user_image.h"
 #include "components/user_manager/user_info.h"
 #include "components/user_manager/user_manager_export.h"
@@ -92,7 +93,7 @@ class USER_MANAGER_EXPORT User : public UserInfo {
   base::string16 GetDisplayName() const override;
   base::string16 GetGivenName() const override;
   const gfx::ImageSkia& GetImage() const override;
-  std::string GetUserID() const override;
+  UserID GetUserID() const override;
 
   // Allows managing child status of the user. Used for RegularUser.
   virtual void SetIsChild(bool is_child);
@@ -175,11 +176,11 @@ class USER_MANAGER_EXPORT User : public UserInfo {
   friend class chromeos::UserAddingScreenTest;
 
   // Do not allow anyone else to create new User instances.
-  static User* CreateRegularUser(const std::string& email);
+  static User* CreateRegularUser(const UserID& email);
   static User* CreateGuestUser();
-  static User* CreateKioskAppUser(const std::string& kiosk_app_username);
-  static User* CreateSupervisedUser(const std::string& username);
-  static User* CreatePublicAccountUser(const std::string& email);
+  static User* CreateKioskAppUser(const UserID& kiosk_app_username);
+  static User* CreateSupervisedUser(const UserID& username);
+  static User* CreatePublicAccountUser(const UserID& email);
 
   explicit User(const std::string& email);
   ~User() override;