Allow Observatory debugger to switch isolates.

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

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="action_link.html">
 <link rel="import" href="function_ref.html">
 <link rel="import" href="isolate_ref.html">
 <link rel="import" href="observatory_element.html">
 <link rel="import" href="script_inset.html">
 <link rel="import" href="script_ref.html">
 <polymer-element name="isolate-summary" extends="observatory-element">
   <template>
     <link rel="stylesheet" href="css/shared.css">
     <div class="flex-row">
       <div class="flex-item-10-percent">
         <img src="img/isolate_icon.png">
       </div>
       <div class="flex-item-10-percent">
+        {{ isolate.number }}
+      </div>
+      <div class="flex-item-20-percent">
         <isolate-ref ref="{{ isolate }}"></isolate-ref>
       </div>
       <div class="flex-item-10-percent">
         <isolate-run-state isolate="{{ isolate }}"></isolate-run-state>
       </div>
-      <div class="flex-item-60-percent">
+      <div class="flex-item-40-percent">
         <isolate-location isolate="{{ isolate }}"></isolate-location>
         [<a on-click="{{ goto }}" _href="{{ gotoLink('/debugger', isolate) }}">debug</a>]
       </div>
       <div class="flex-item-10-percent">
       </div>
     </div>
 
     <div class="flex-row">
       <div class="flex-item-20-percent"></div>
       <div class="flex-item-60-percent">
@@ skipping 158 matching lines @@
   </template>
 </polymer-element>
 
 <polymer-element name="isolate-counter-chart" extends="observatory-element">
   <template>
     <div id="counterPieChart" style="height: 200px"></div>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="isolate_summary.dart"></script>