Collect samples for background threads.

runtime/observatory/web/timeline.js

 // Copyright (c) 2015, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 function onModelLoaded() {
   viewer.globalMode = true;
   viewer.model = model;
 }
 
 function clearTimeline() {
@@ skipping 37 matching lines @@
   pendingRequests--;
   if (pendingRequests == 0) {
     console.log("Got all timeline parts");
     updateTimeline(traceObject);
   }
 }
 
 function fetchTimelineOnLoad(event) {
   var xhr = event.target;
   var response = JSON.parse(xhr.responseText);
-  var result = response['result'];
-  var newStackFrames = result['stackFrames'];  // Map.
-  var newTraceEvents = result['traceEvents'];  // List.
 
-  // Merge in timeline events.
-  traceObject.traceEvents = traceObject.traceEvents.concat(newTraceEvents);
-  for (var key in newStackFrames) {
-    if (newStackFrames.hasOwnProperty(key)) {
-      traceObject.stackFrames[key] = newStackFrames[key];
+  if (response.error) {
+    // Maybe profiling is disabled.
+    console.log("ERROR " + response.error.message);
+  } else {
+    var result = response['result'];
+    var newStackFrames = result['stackFrames'];  // Map.
+    var newTraceEvents = result['traceEvents'];  // List.
+
+    // Merge in timeline events.
+    traceObject.traceEvents = traceObject.traceEvents.concat(newTraceEvents);
+    for (var key in newStackFrames) {
+      if (newStackFrames.hasOwnProperty(key)) {
+        traceObject.stackFrames[key] = newStackFrames[key];
+      }
     }
   }
 
   gotReponse();
 }
 
 function fetchTimelineOnError(event) {
   var xhr = event.target;
   console.log(xhr.statusText);
   gotReponse();
@@ skipping 135 matching lines @@
   viewer = document.createElement('tr-ui-timeline-view');
   viewer.track_view_container = container;
   viewer.appendChild(container);
   viewer.id = 'trace-viewer';
   viewer.globalMode = true;
   document.body.appendChild(viewer);
   registerForMessages();
 });
 
 console.log('loaded');