Give instances their own model class; move DartErrors out of instance-ref into their own error-ref.

runtime/bin/vmservice/observatory/lib/src/elements/library_view.html

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="class_ref.html">
 <link rel="import" href="curly_block.html">
 <link rel="import" href="eval_box.html">
 <link rel="import" href="field_ref.html">
 <link rel="import" href="function_ref.html">
 <link rel="import" href="instance_ref.html">
 <link rel="import" href="observatory_element.html">
 <link rel="import" href="library_ref.html">
 <link rel="import" href="nav_bar.html">
@@ skipping 86 matching lines @@
         variables ({{ library.variables.length }})
         <curly-block expand="{{ library.variables.length <= 8 }}">
           <div class="memberList">
             <template repeat="{{ field in library.variables }}">
               <div class="memberItem">
                 <div class="memberName">
                   <field-ref ref="{{ field }}"></field-ref>
                 </div>
                 <div class="memberValue">
                   <template if="{{ field['value'] != null }}">
-                    <instance-ref ref="{{ field['value'] }}"></instance-ref>
+                    <any-service-ref ref="{{ field['value'] }}"></any-service-ref>
                   </template>
                 </div>
               </div>
             </template>
           </div>
         </curly-block><br>
         <br>
       </template>
 
       <template if="{{ library.functions.isNotEmpty }}">
@@ skipping 17 matching lines @@
 
     <div class="content">
       <eval-box callback="{{ eval }}"></eval-box>
     </div>
     <br><br><br><br>
     <br><br><br><br>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="library_view.dart"></script>