Rework error handling in the service protocol and in Observatory.

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

 <link rel="import" href="../../../../packages/polymer/polymer.html">
 <link rel="import" href="code_ref.html">
 <link rel="import" href="function_ref.html">
 <link rel="import" href="nav_bar.html">
 <link rel="import" href="observatory_element.html">
 <link rel="import" href="sliding_checkbox.html">
 <link rel="import" href="view_footer.html">
 
 <polymer-element name="cpu-profile-table" extends="observatory-element">
   <template>
     <link rel="stylesheet" href="css/shared.css">
     <nav-bar>
       <top-nav-menu></top-nav-menu>
       <vm-nav-menu vm="{{ isolate.vm }}"></vm-nav-menu>
       <isolate-nav-menu isolate="{{ isolate }}"></isolate-nav-menu>
       <nav-menu link="{{ makeLink('/profiler-table', isolate) }}" anchor="cpu profile (table)" last="{{ true }}"></nav-menu>
       <nav-refresh callback="{{ refresh }}"></nav-refresh>
-      <nav-refresh callback="{{ clear }}" label="Clear"></nav-refresh>
+      <nav-refresh callback="{{ clearCpuProfile }}" label="Clear"></nav-refresh>
     </nav-bar>
     <style>
       /* general */
       .well {
         background-color: #ECECEC;
         padding: 0.2em;
       }
       .center {
         align-items: center;
         justify-content: center;
@@ skipping 114 matching lines @@
       <template if="{{ state == 'Requested' }}">
         <div class="statusBox shadow center">
           <div class="statusMessage">Fetching profile from VM...</div>
         </div>
       </template>
       <template if="{{ state == 'Loading' }}">
         <div class="statusBox shadow center">
           <div class="statusMessage">Loading profile...</div>
         </div>
       </template>
+      <template if="{{ state == 'Disabled' }}">
+        <div class="statusBox shadow center">
+          <div>
+            <h1>Profiling is disabled</h1>
+            <br>
+            Perhaps the <b>profile</b> flag has been disabled for this VM.
+            <br><br>
+            See all
+            <a on-click="{{ goto }}" _href="{{ gotoLink('/flags') }}">vm flags</a>
+          </div>
+        </div>
+      </template>
       <template if="{{ state == 'Exception' }}">
         <div class="statusBox shadow center">
           <div class="statusMessage">
-            <h1>Exception:</h1>
+            <h1>Profiling is disabled due to unexpected exception:</h1>
             <br>
             <pre>{{ exception.toString() }}</pre>
             <br>
             <h1>Stack trace:</h1>
             <br>
             <pre>{{ stackTrace.toString() }}</pre>
           </div>
         </div>
       </template>
       <template if="{{ state == 'Loaded' }}">
@@ skipping 107 matching lines @@
 
 <polymer-element name="cpu-profile" extends="observatory-element">
   <template>
     <link rel="stylesheet" href="css/shared.css">
     <nav-bar>
       <top-nav-menu></top-nav-menu>
       <vm-nav-menu vm="{{ isolate.vm }}"></vm-nav-menu>
       <isolate-nav-menu isolate="{{ isolate }}"></isolate-nav-menu>
       <nav-menu link="{{ makeLink('/profiler', isolate) }}" anchor="cpu profile" last="{{ true }}"></nav-menu>
       <nav-refresh callback="{{ refresh }}"></nav-refresh>
-      <nav-refresh callback="{{ clear }}" label="Clear"></nav-refresh>
+      <nav-refresh callback="{{ clearCpuProfile }}" label="Clear"></nav-refresh>
     </nav-bar>
     <style>
       .tableWell {
         background-color: #ECECEC;
         padding: 0.2em;
       }
 
       .table {
         border-spacing: 0px;
         width: 100%;
@@ skipping 70 matching lines @@
       <template if="{{ state == 'Requested' }}">
         <div class="statusBox shadow center">
           <div class="statusMessage">Fetching profile from VM...</div>
         </div>
       </template>
       <template if="{{ state == 'Loading' }}">
         <div class="statusBox shadow center">
           <div class="statusMessage">Loading profile...</div>
         </div>
       </template>
+      <template if="{{ state == 'Disabled' }}">
+        <div class="statusBox shadow center">
+          <div>
+            <h1>Profiling is disabled</h1>
+            <br>
+            Perhaps the <b>profile</b> flag has been disabled for this VM.
+            <br><br>
+            See all
+            <a on-click="{{ goto }}" _href="{{ gotoLink('/flags') }}">vm flags</a>
+          </div>
+        </div>
+      </template>
       <template if="{{ state == 'Exception' }}">
         <div class="statusBox shadow center">
           <div class="statusMessage">
-            <h1>Exception:</h1>
+            <h1>Profiling is disabled due to unexpected exception:</h1>
             <br>
             <pre>{{ exception.toString() }}</pre>
             <br>
             <h1>Stack trace:</h1>
             <br>
             <pre>{{ stackTrace.toString() }}</pre>
           </div>
         </div>
       </template>
       <template if="{{ state == 'Loaded' }}">
@@ skipping 76 matching lines @@
           <tbody id="treeBody">
           </tbody>
         </table>
       </div>
     </div>
     <view-footer></view-footer>
   </template>
 </polymer-element>
 
 <script type="application/dart" src="cpu_profile.dart"></script>