Improve behaviour when we hit a stack overflow / OOM error

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">
@@ skipping 46 matching lines @@
 
       <template if="{{ isolate.pauseEvent.kind == 'PauseInterrupted' ||
                        isolate.pauseEvent.kind == 'PauseBreakpoint' ||
                        isolate.pauseEvent.kind == 'PauseException' }}">
         <template if="{{ isolate.pauseEvent.breakpoint != null }}">
           by breakpoint
         </template>
         <template if="{{ isolate.pauseEvent.kind == 'PauseException' }}">
           by exception
         </template>
-        at
-        <function-ref ref="{{ isolate.topFrame.function }}">
-        </function-ref>
-        (<source-link location="{{ isolate.topFrame.location }}">
-        </source-link>)
+        <template if="{{ isolate.topFrame != null }}">
+          at
+          <function-ref ref="{{ isolate.topFrame.function }}">
+          </function-ref>
+          (<source-link location="{{ isolate.topFrame.location }}">
+          </source-link>)
+        </template>
       </template>
     </template>
 
     <template if="{{ isolate.running }}">
       at
       <function-ref ref="{{ isolate.topFrame.function }}">
       </function-ref>
       (<source-link location="{{ isolate.topFrame.location }}"></source-link>)
     </template>
 
@@ skipping 131 matching lines @@
     <div class="chart-wrapper" id="isolate-counter-chart">
       <div class="chart-host-wrapper">
         <div class="chart-host" id="isolate-counter-chart-host"></div>
         <div class="chart-legend-host" id="isolate-counter-chart-legend-host"></div>
       </div>
   </div>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="isolate_summary.dart"></script>