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

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

Index: chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
diff --git a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
index 40b2eeffe476b737f3cb2ffd836f865964759f4b..6192c72e166e1ddc6b7ad4984b648054a2bbc1fb 100644
--- a/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
+++ b/chrome/browser/ui/webui/chromeos/login/signin_screen_handler.cc
@@ -852,6 +852,10 @@ void SigninScreenHandler::RegisterMessages() {
   AddCallback("updateOfflineLogin",
               &SigninScreenHandler::HandleUpdateOfflineLogin);
   AddCallback("focusPod", &SigninScreenHandler::HandleFocusPod);
+
+  // This message is sent by the kiosk app menu, but is handled here
+  // so we can tell the delegate to launch the app.
+  AddCallback("launchKioskApp", &SigninScreenHandler::HandleLaunchKioskApp);
 }
 
 void SigninScreenHandler::RegisterPrefs(PrefRegistrySimple* registry) {
@@ -1626,6 +1630,10 @@ void SigninScreenHandler::HandleFocusPod(const std::string& user_id) {
   SetUserInputMethod(user_id);
 }
 
+void SigninScreenHandler::HandleLaunchKioskApp(const std::string& app_id) {
+  delegate_->LoginAsKioskApp(app_id);
+}
+
 void SigninScreenHandler::StartClearingDnsCache() {
   if (dns_clear_task_running_ || !g_browser_process->io_thread())
     return;