Add <sky-icon> to access material design widgets

sky/examples/stocks/stocks.sky

 <!--
 // 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.
 -->
 <import src="/sky/framework/sky-drawer.sky" />
 <import src="/sky/framework/sky-element.sky" />
+<import src="/sky/framework/sky-icon.sky" />
 <import src="/sky/framework/sky-scrollable.sky" />
 <import src="stock.sky" as='view'/>
 <import src='companylist.sky' as='model'/>
 
 <sky-element>
 <template>
   <style>
     :host {
       display: flex;
       flex-direction: column;
@@ skipping 13 matching lines @@
       display: flex;
       align-items: center;
       background-color: #526E9C;
       color: white;
       height: 56px;
     }
     #menu {
       display: flex;
       justify-content: center;
       align-items: center;
-      width: 24px;
-      height: 24px;
       padding: 7px;
       margin: 0 8px;
-      background-color: papayawhip;
       color: black;
     }
     #title {
       flex: 1;
       margin: 0 8px;
     }
     sky-scrollable {
       flex: 1;
     }
   </style>
   <sky-drawer id="drawer">
     I am drawer
   </sky-drawer>
   <sky-toolbar>
-    <div id="menu" />
+    <sky-icon id="menu" type="navigation/menu_white" size="24" />
     I am a stocks app
   </sky-toolbar>
   <sky-scrollable id='stock_list'>
   </sky-scrollable>
 </template>
 <script>
 import "dart:sky";
 import "dart:math";
 
 List pick(List list, int count) {
@@ skipping 27 matching lines @@
   }
 
   void _handleMenuClick(_) {
     _drawer.toggle();
   }
 }
 
 _init(script) => register(script, Stocks);
 </script>
 </sky-element>