[ChromeOS] Reset Gaia UI and show error if needed.

chrome/browser/resources/chromeos/login/screen_gaia_signin.js

Index: chrome/browser/resources/chromeos/login/screen_gaia_signin.js
diff --git a/chrome/browser/resources/chromeos/login/screen_gaia_signin.js b/chrome/browser/resources/chromeos/login/screen_gaia_signin.js
index 6df1a5cd62bbcb3dc7502903318ae8e4bd577bbe..3a3bc48c4a6f28c6ad4479f655166a78d63480e4 100644
--- a/chrome/browser/resources/chromeos/login/screen_gaia_signin.js
+++ b/chrome/browser/resources/chromeos/login/screen_gaia_signin.js
@@ -79,6 +79,15 @@ cr.define('login', function() {
       if (msg.method == 'completeLogin' && this.isAuthExtMessage_(e)) {
         chrome.send('completeLogin', [msg.email, msg.password] );
       }
+    },
+
+    /**
+     * Clears input fields and switches to input mode.
+     * @param {boolean} takeFocus True to take focus.
+     */
+    reset: function(takeFocus) {
+      // Reload and show the sign-in UI.
+      Oobe.showSigninUI();
     }
   };