MD WebUI: Add shared cr-toolbar element

ui/webui/resources/cr_elements/cr_toolbar/cr_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: 'cr-toolbar',
+
+  properties: {
+    narrow_: {
+      type: Boolean,
+      reflectToAttribute: true
+    },
+    showingSearch_: {
+      type: Boolean,
+      reflectToAttribute: true,
+    },
+    // Name to display in the toolbar, in titlecase.
+    pageName: String,
+    // Prompt text to display in the search field.
+    searchPrompt: String,
+    // Tooltip to display on the clear search button.
+    clearLabel: String,
+  },
+
+  /** @return {CrToolbarSearchFieldElement} */
+  getSearchField: function() {
+    return this.$.search;
+  }
+});