MD History: Hook all elements into the page and add tests.

chrome/browser/resources/md_history/history_toolbar.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.
+
+Polymer({
+  is: 'history-toolbar',
+  properties: {
+    // Number of history items currently selected.
+    count: {
+      type: Number,
+      value: 0,
+      observer: 'changeToolbarView_'
+    },
+    // True if 1 or more history items are selected. When this value changes
+    // the background colour changes.
+    itemsSelected_: {
+      type: Boolean,
+      value: false,
+      reflectToAttribute: true
+    }
+  },
+
+  /**
+   * This function changes the toolbar background color depending on whether or

[tsergeant, 2016/01/22 02:37:11]

Remove "this function" (it's implied):

Change the toolbar background color depending on whether any history
items are currently selected.

+   * not any history items are currently selected.
+   * @private
+   */
+  changeToolbarView_: function() {
+    this.itemsSelected_ = this.count != 0;
+  },
+
+  clearSelection: function() {
+    this.fire('unselect-all');
+  }
+});