[Search] Make the text swoosh away off the screen when the user taps the opt-in link.

chrome/browser/resources/contextual_search/promo.js

 /* Copyright 2014 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.
-   TODO(mathp): Add some JS here.
 */
+
+/**
+ * On load, registers the handler to add the 'hide' class to the container
+ * element in order to hide it.
+ */
+window.onload = function() {
+  $('optin-label').addEventListener('click', function() {
+    $('container').classList.add('hide');
+  });
+};