Teach the Observatory about WeakProperties (ephemerons).

runtime/bin/vmservice/observatory/lib/src/elements/instance_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="instance-ref" extends="service-ref">
   <template>
     <link rel="stylesheet" href="css/shared.css">
     <style>
       .errorBox {
@@ skipping 52 matching lines @@
               <div class="memberItem">
                 <div class="memberName">[{{ element['index']}}]</div>
                 <div class="memberValue">
                   <any-service-ref ref="{{ element['value'] }}"></any-service-ref>
                 </div>
               </div>
             </template>
           </div>
         </curly-block>
       </template>
+
+      <template if="{{ ref.isWeakProperty }}">
+        <a on-click="{{ goto }}" _href="{{ url }}"><em>{{ ref.clazz.name }}</em></a>
+        <curly-block callback="{{ expander() }}">
+          <div class="memberList">
+            <div class="memberItem">
+              <div class="memberName">key</div>
+              <div class="memberValue">
+                <any-service-ref ref="{{ ref.key }}"></any-service-ref>
+              </div>
+            </div>
+            <div class="memberItem">
+              <div class="memberName">value</div>
+              <div class="memberValue">
+                <any-service-ref ref="{{ ref.value }}"></any-service-ref>
+              </div>
+            </div>
+          </div>
+        </curly-block>
+      </template>
     </span>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="instance_ref.dart"></script>