cros: Pass gaia_auth init params via postMessage.

chrome/browser/resources/gaia_auth/offline.js

 // Copyright (c) 2012 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.
 
 /**
  * @fileoverview Offline login implementation.
  */
 
-function load() {
-  var params = getUrlSearchParams(location.search);
-
+/**
+ * Initialize the offline page.
+ * @param {Object} params Intialization params passed from parent page.
+ */
+function load(params) {
   // Setup localized strings.
   $('sign-in-title').textContent = decodeURIComponent(params['stringSignIn']);
   $('email-label').textContent = decodeURIComponent(params['stringEmail']);
   $('password-label').textContent =
       decodeURIComponent(params['stringPassword']);
   $('submit-button').value = decodeURIComponent(params['stringSignIn']);
   $('empty-email-alert').textContent =
       decodeURIComponent(params['stringEmptyEmail']);
   $('empty-password-alert').textContent =
       decodeURIComponent(params['stringEmptyPassword']);
@@ skipping 30 matching lines @@
     // made. Try to mimic Gaia's behaviour.
     form.email.value = email;
     form.password.classList.add('form-error');
     form.password.focus();
   } else {
     form.email.focus();
   }
   window.parent.postMessage({'method': 'loginUILoaded'}, 'chrome://oobe/');
 }
 
-document.addEventListener('DOMContentLoaded', load);
+/**
+ * Handles initialization message from parent page.
+ * @param {MessageEvent} e
+ */
+function handleInitializeMessage(e) {
+  var ALLOWED_PARENT_ORIGINS = [
+    'chrome://oobe',
+    'chrome://chrome-signin'
+  ];
+
+  if (ALLOWED_PARENT_ORIGINS.indexOf(e.origin) == -1)
+    return;
+
+  window.removeEventListener('message', handleInitializeMessage);
+
+  var params = e.data;
+  params.parentPage = e.origin;
+  load(params);
+}
+
+document.addEventListener('DOMContentLoaded', function() {
+  window.addEventListener('message', handleInitializeMessage);
+});