Service cleanups...

runtime/observatory/lib/src/elements/context_ref.html

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="curly_block.html">
 <link rel="import" href="observatory_element.html">
 <link rel="import" href="service_ref.html">
 
 <polymer-element name="context-ref" extends="service-ref">
   <template>
     <link rel="stylesheet" href="css/shared.css">
     <span>
       <a on-click="{{ goto }}" _href="{{ url }}"><em>Context</em> ({{ ref.length }})</a>
       <curly-block callback="{{ expander() }}">
         <div class="memberList">
           <div class="memberItem">
             <div class="memberName">parent</div>
             <div class="memberValue">
               <any-service-ref ref="{{ ref.parentContext }}"></any-service-ref>
             </div>
           </div>
-          <template repeat="{{ variable in ref.variables }}">
+          <template repeat="{{ index in ref.variables.asMap().keys }}">
             <div class="memberItem">
-              <div class="memberName">[{{ variable['index']}}]</div>
+              <div class="memberName">[{{ index }}]</div>
               <div class="memberValue">
-                <any-service-ref ref="{{ variable['value'] }}"></any-service-ref>
+                <any-service-ref ref="{{ ref.variables[index]['value'] }}">
+                </any-service-ref>
               </div>
             </div>
           </template>
         </div>
       </curly-block>
     </span>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="context_ref.dart"></script>