Add FakeChromeEvent

chrome/test/data/webui/fake_chrome_event.js

+// Copyright 2015 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 Fake implementations of ChromeEvent.
+ */
+
+/**
+ * @constructor
+ * @extends {ChromeEvent}
+ */
+function FakeChromeEvent() {
+  /** @type {!Set<!Function>} */
+  this.listeners_ = new Set;

[dpapad, 2015/12/17 00:04:18]

Nit: Can we use the following syntax?

this.listeners_ = new Set();
I have not encountered the syntax with the omitted () in Chromium's codebase.

[stevenjb, 2015/12/17 00:18:11]

Sure. That's just my C background (and newness to JS) showing through :)

+}
+
+FakeChromeEvent.prototype = {
+  /** @param {Function} listener */
+  addListener: function(listener) {

[dschuyler, 2015/12/16 22:27:03]

Maybe: since this is now a Set and therefore should not allow a listener to be
added twice, could we assert or 'expect' that here?
assertFalse(this.listeners_.has(listener));

[stevenjb, 2015/12/17 00:18:11]

Done.

+    this.listeners_.add(listener);
+  },
+
+  /** @param {Function} listener */
+  removeListener: function(listener) {
+    if (!this.listeners_.has(listener)) {
+      console.error('removeListener: not found');
+      return;
+    }
+    this.listeners_.delete(listener);
+  },
+
+  /** @param {...} args */
+  callListeners: function(...args) {
+    this.listeners_.forEach(function(l) {
+      l.apply(null, args);
+    });
+  }
+};