Improve display of simd vector types and stack traces in Observatory.

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

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="curly_block.html">
 <link rel="import" href="observatory_element.html">
 <link rel="import" href="service_ref.html">
 
 <polymer-element name="instance-ref" extends="service-ref">
   <template>
     <link rel="stylesheet" href="css/shared.css">
     <style>
       .indented {
         margin-left: 1.5em;
         font: 400 14px 'Montserrat', sans-serif;
         line-height: 150%;
       }
+      .stackTraceBox {
+        margin-left: 1.5em;
+        background-color: #f5f5f5;
+        border: 1px solid #ccc;
+        padding: 10px;
+        font-family: consolas, courier, monospace;
+        font-size: 12px;
+        white-space: pre;
+        overflow-x: auto;
+      }
     </style>
     <span>
       <template if="{{ ref.isSentinel }}">
         <span title="{{ hoverText }}">{{ ref.valueAsString }}</span>
       </template>
 
       <template if="{{ ref.isBool || ref.isInt ||
-                       ref.isDouble || ref.isNull }}">
+                       ref.isDouble || ref.isSimdValue ||
+                       ref.isNull }}">
         <a on-click="{{ goto }}" _href="{{ url }}">{{ ref.valueAsString }}</a>
       </template>
 
+      <template if="{{ ref.isStackTrace }}">
+        <a on-click="{{ goto }}" _href="{{ url }}"><em>{{ ref.clazz.name }}</em></a>
+        <curly-block expandKey="{{ expandKey }}">
+          <div class="stackTraceBox">{{ ref.valueAsString }}</div>
+        </curly-block>
+      </template>
+
       <template if="{{ ref.isString }}">
         <a on-click="{{ goto }}" _href="{{ url }}">{{ asStringLiteral(ref.valueAsString, ref.valueAsStringIsTruncated) }}</a>
       </template>
 
 
       <template if="{{ ref.isAbstractType }}">
         <a on-click="{{ goto }}" _href="{{ url }}">{{ ref.name }}</a>
       </template>
 
       <template if="{{ ref.isClosure }}">
@@ skipping 90 matching lines @@
                              expandKey="{{ makeExpandKey('value') }}">
             </any-service-ref><br>
           </div>
         </curly-block>
       </template>
     </span>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="instance_ref.dart"></script>