[MD Bookmarks] Add skeleton for MD Bookmarks.

chrome/browser/resources/md_bookmarks/toolbar.js

+// Copyright 2016 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: 'bookmarks-toolbar',
+
+  /**
+   * @param {Event} e
+   * @private
+   */
+  onMenuButtonOpenTap_: function(e) {
+    var menu = /** @type {!CrActionMenuElement} */ (this.$.dropdown);
+    menu.showAt(/** @type {!Element} */ (e.target));
+  },
+
+  /** @private */
+  onBulkEditTap_: function() {
+    this.closeDropdownMenu_();
+  },
+
+  /** @private */
+  onSortTap_: function() {
+    this.closeDropdownMenu_();
+  },
+
+  /** @private */
+  onAddBookmarkTap_: function() {
+    this.closeDropdownMenu_();
+  },
+
+  /** @private */
+  onAddImportTap_: function() {
+    this.closeDropdownMenu_();
+  },
+
+  /** @private */
+  onAddExportTap_: function() {
+    this.closeDropdownMenu_();
+  },
+
+  /** @private */
+  closeDropdownMenu_: function() {
+    var menu = /** @type {!CrActionMenuElement} */ (this.$.dropdown);
+    menu.close();
+  }
+});