Refactor kiosk app launch to be part of login screen UI flow.

chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
index 1d51afc93f730330ec644d03f4edc3c1dc79e494..034f3da63d49fe9d73116d4d4a505571eb84d583 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.h
@@ -157,6 +157,9 @@ class SigninScreenHandlerDelegate {
   // Signs out if the screen is currently locked.
   virtual void Signout() = 0;
 
+  // Launches kiosk app with given |app_id|.
+  virtual void LaunchKioskApp(const std::string& app_id) = 0;
+
  protected:
   virtual ~SigninScreenHandlerDelegate() {}
 };
@@ -326,6 +329,7 @@ class SigninScreenHandler
   void HandleShowLoadingTimeoutError();
   void HandleUpdateOfflineLogin(bool offline_login_active);
   void HandleShowLocallyManagedUserCreationScreen();
+  void HandleLaunchKioskApp(const std::string& app_id);
 
   // Fills |user_dict| with information about |user|.
   static void FillUserDictionary(User* user,