Files.app: Add a unit test of ProgressCenterHandler class.

chrome/test/data/file_manager/unit_tests/mocks/mock_progress_center.js

+// Copyright 2013 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.
+'use strict';
+
+/**
+ * Mock of Progress Center.
+ * @constructor
+ */
+function MockProgressCenter() {
+  /**
+   * Items stored in the progress center.
+   * @type {Object.<string, ProgressCenterItem>}
+   */
+  this.items = {};
+
+  Object.seal(this);
+}
+
+/**
+ * Stores an item to the progress center.
+ * @param {ProgressCenterItem} item Progress center item to be stored.
+ */
+MockProgressCenter.prototype.updateItem = function(item) {
+  this.items[item.id] = item;
+};
+
+/**
+ * Obtains an item stored in the progress center.
+ * @param {string} id ID spcifying the progress item.
+ */
+MockProgressCenter.prototype.getItemById = function(id) {
+  return this.items[id];
+};