Dramatically increase the performance of Observatory's profile UI

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

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="action_link.html">
 <link rel="import" href="observatory_element.html">
 
 <polymer-element name="nav-bar" extends="observatory-element">
   <template>
     <link rel="stylesheet" href="css/shared.css">
     <style>
       nav {
         position: fixed;
@@ skipping 368 matching lines @@
 
 <polymer-element name="nav-notify-exception" extends="observatory-element">
   <template>
     <style>
       .item {
         position: relative;
         padding: 16px;
         margin-top: 10px;
         margin-right: 10px;
         padding-right: 25px;
-        width: 250px;
+        width: 500px;
         color: #ddd;
         background: rgba(0,0,0,.6);
         border: solid 2px white;
         box-shadow: 0 0 5px black;
         border-radius: 5px;
         animation: fadein 1s;
       }
 
       @keyframes fadein {
         from { opacity: 0; }
@@ skipping 21 matching lines @@
         line-height: 16px;
         border-radius: 9px;
         color: white;
         font-size: 18px;
         cursor: pointer;
         text-align: center;
       }
       a.boxclose:hover {
         background: rgba(255,255,255,0.5);
       }
+      .stacktrace {
+        white-space: pre
+      }
     </style>
     <template if="{{ isUnexpectedError }}">
       <!-- TODO(turnidge): Add a file-a-bug link to this notification -->
       <div class="item">
         Unexpected exception:<br><br>
         <div class="indent">{{ exception.toString() }}</div><br>
         <template if="{{ stacktrace != null }}">
           Stacktrace:<br><br>
-          <div class="indent">{{ stacktrace.toString() }}</div>
+          <div class="indent stacktrace">{{ stacktrace.toString() }}</div>
           <br>
         </template>
         [<a class="link" on-click="{{ goto }}"
             _href="{{ gotoLink('vm-connect') }}">Connect to a different VM</a>]
         <a class="boxclose" on-click="{{ closeItem }}">&times;</a>
     </div>
     </template>
     <template if="{{ isNetworkError }}">
       <div class="item">
         The request cannot be completed because the VM is currently
         disconnected.
         <br><br>
         [<a class="link" on-click="{{ goto }}"
             _href="{{ gotoLink('vm-connect') }}">Connect to a different VM</a>]
         <a class="boxclose" on-click="{{ closeItem }}">&times;</a>
     </div>
     </template>
   </template>
 </polymer-element>
 
 
 <script type="application/dart" src="nav_bar.dart"></script>