add a div around the label so we can do text-overflow: ellipsis

Author: Yvonne Yip

core-item.html

@@ -35,7 +35,9 @@
 <polymer-element name="core-item" attributes="label icon src" horizontal center layout>
 <template>
 
-  <core-icon src="{{src}}" icon="{{icon}}" hidden?="{{!src && !icon}}"></core-icon>{{label}}<content></content>
+  <core-icon src="{{src}}" icon="{{icon}}" hidden?="{{!src && !icon}}"></core-icon>
+  <div id="label">{{label}}</div>
+  <content></content>
 
 </template>
 <script>