Add a box-shadow to the app-bar per material design

sky/examples/stocks/stock.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-element.sky" />
 
 <sky-element>
 <template>
   <style>
@@ skipping 10 matching lines @@
   }
   #ticker {
     flex-grow: 1;
   }
   #last-sale {
     padding-right: 20px;
   }
   #change {
     border-radius: 5px;
     min-width: 72px;
+    padding: 2px;
     padding-right: 10px;
     text-align: right;
   }
   </style>
   <div id="ticker" />
   <div id="last-sale" />
   <div id="change" />
 </template>
 <script>
 import "dart:sky";
@@ skipping 52 matching lines @@
     if (model.percentChange > 0)
       changeString = "+" + changeString;
     change.textContent = changeString;
     change.style['background-color'] = colorForPercentChange(model.percentChange);
   }
 }
 
 _init(script) => register(script, Stock);
 </script>
 </sky-element>