2nd attempt at adding streamListen/streamCancel to the service protocol.

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

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="class_ref.html">
 <link rel="import" href="field_ref.html">
 <link rel="import" href="function_ref.html">
 <link rel="import" href="instance_ref.html">
 <link rel="import" href="observatory_element.html">
 <link rel="import" href="nav_bar.html">
 <link rel="import" href="object_common.html">
 <link rel="import" href="context_ref.html">
 <link rel="import" href="view_footer.html">
@@ skipping 13 matching lines @@
 
     <template if="{{ !context.isError }}">
       <div class="content">
         <h1>instance of Context</h1>
 
         <object-common object="{{ context }}"></object-common>
 
         <div class="memberList">
           <div class="memberItem">&nbsp;</div>
 
-          <div class="memberItem">
-            <div class="memberName">parent context</div>
-            <div class="memberValue">
-              <any-service-ref ref="{{ context.parentContext }}"></any-service-ref>
+          <template if="{{ context.parentContext != null }}">
+            <div class="memberItem">
+              <div class="memberName">parent context</div>
+              <div class="memberValue">
+                <any-service-ref ref="{{ context.parentContext }}"></any-service-ref>
+              </div>
             </div>
-          </div>
+          </template>
         </div>
       </div>
 
       <hr>
 
       <div class="content">
         <template if="{{ context.variables.isNotEmpty }}">
           variables ({{ context.variables.length }})
           <curly-block expand="{{ context.variables.length <= 8 }}">
             <div class="memberList">
               <template repeat="{{ index in context.variables.asMap().keys }}">
                 <div class="memberItem">
                   <div class="memberName">[{{ index }}]</div>
                   <div class="memberValue">
                     <any-service-ref
-                       ref="{{ context.variables[index]{'value'] }}">
+                       ref="{{ context.variables[index]['value'] }}">
                     </any-service-ref>
                   </div>
                 </div>
               </template>
             </div>
           </curly-block><br><br>
         </template>
       </div>
     </template>
     <view-footer></view-footer>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="context_view.dart"></script>