When attempting to navigate to a page for an isolate that doesn't exist, offer to

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

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="observatory_element.html">
 
 <polymer-element name="script-inset" extends="observatory-element">
   <template>
     <style>
       .sourceInset {
       }
       .sourceTable {
       display: table;
       background-color: #f5f5f5;
       border: 1px solid #ccc;
       padding: 10px;
       overflow-y: auto;
       width: 100%;
+      box-sizing: border-box;
       }
       .sourceRow {
       display: table-row;
       }
       .sourceItem, .sourceItemCurrent {
       display: table-cell;
       vertical-align: top;
       font: 400 14px consolas, courier, monospace;
       line-height: 125%;
       white-space: pre;
@@ skipping 45 matching lines @@
       }
       .resolvedBreakpoint {
         color: white;
         background-color: #e66;
       }
     </style>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="script_inset.dart"></script>