Make retained size human-readable.

runtime/bin/vmservice/client/lib/src/elements/instance_view.html

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="class_ref.html">
 <link rel="import" href="error_view.html">
 <link rel="import" href="eval_box.html">
 <link rel="import" href="eval_link.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">
@@ skipping 38 matching lines @@
               <div class="memberValue">{{ instance['valueAsString'] }}</div>
             </div>
           </template>
           <div class="memberItem">
             <div class="memberName">size</div>
             <div class="memberValue">{{ instance['size'] | formatSize }}</div>
           </div>
           <div class="memberItem">
             <div class="memberName">retained size</div>
             <div class="memberValue">
-              <eval-link callback="{{ retainedSize }}"
-                         label="[calculate]">
-              </eval-link>
+              <template if="{{ retainedBytes == null }}">
+                <eval-link callback="{{ retainedSize }}"
+                           label="[calculate]">
+                </eval-link>
+              </template>
+              <template if="{{ retainedBytes != null }}">
+                {{ retainedBytes | formatSize }}
+              </template>
             </div>
           </div>
           <div class="memberItem">
             <div class="memberName">retaining path</div>
             <div class="memberValue">
               <template if="{{ path == null }}">
                 <eval-link callback="{{ retainingPath }}"
                            label="[find]"
                            expr="10">
                 </eval-link>
@@ skipping 107 matching lines @@
         <eval-box callback="{{ eval }}"></eval-box>
       </div>
       <br><br><br><br>
       <br><br><br><br>
 
     </template>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="instance_view.dart"></script>