[MD History] Factor out a common HistoryListBehavior.

ui/webui/resources/js/util.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.
 
 // <include src="assert.js">
 
 /**
  * Alias for document.getElementById. Found elements must be HTMLElements.
  * @param {string} id The ID of the element to find.
  * @return {HTMLElement} The found element or null if not found.
@@ skipping 355 matching lines @@
 
 /**
  * Quote a string so it can be used in a regular expression.
  * @param {string} str The source string.
  * @return {string} The escaped string.
  */
 function quoteString(str) {
   return str.replace(/([\\\.\+\*\?\[\^\]\$\(\)\{\}\=\!\<\>\|\:])/g, '\\$1');
 }
 
+/**
+ * Returns a promise which is resolved when |eventName| is fired on |element|
+ * and |predicate| is true.
+ * @param {HTMLElement} element
+ * @param {string} eventName
+ * @param {function(Event): boolean} predicate

[tsergeant, 2016/08/05 01:39:09]

@return {Promise}

[calamity, 2016/08/09 02:56:00]

Done.

+ */
+function waitForEvent(element, eventName, predicate) {

[tsergeant, 2016/08/05 01:39:09]

I can conceive of situations where this would be useful in real code... but
considering at the moment this is only used in a test, I don't think there's any
need to ship this out with every WebUI.

I think we should just put this in test_util for now.

[calamity, 2016/08/09 02:56:00]

Done.

+  if (!predicate)
+    predicate = function() { return true; };
+
+  return new Promise(function(resolve) {
+    var listener = function(e) {
+      if (!predicate(e))
+        return;
+
+      resolve();
+      element.removeEventListener(eventName, listener);
+    }
+
+    element.addEventListener(eventName, listener);
+  });
+}
+
 // <if expr="is_ios">
 // Polyfill 'key' in KeyboardEvent for iOS.
 // This function is not intended to be complete but should
 // be sufficient enough to have iOS work correctly while
 // it does not support key yet.
 if (!('key' in KeyboardEvent.prototype)) {
   Object.defineProperty(KeyboardEvent.prototype, 'key', {
     /** @this {KeyboardEvent} */
     get: function () {
       // 0-9
@@ skipping 46 matching lines @@
         case 0xdb: return '[';
         case 0xdd: return ']';
       }
       return 'Unidentified';
     }
   });
 } else {
   window.console.log("KeyboardEvent.Key polyfill not required");
 }
 // </if>  /* is_ios */