Add request tracing to Observatory:

runtime/bin/vmservice/observatory/lib/src/elements/stack_frame.dart

 // Copyright (c) 2013, 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.
 
 library stack_frame_element;
 
 import 'observatory_element.dart';
 import 'package:polymer/polymer.dart';
 
 @CustomTag('stack-frame')
 class StackFrameElement extends ObservatoryElement {
   @published ObservableMap frame;
+  @published bool expand = false;
   StackFrameElement.created() : super.created();
+
+  dynamic expander() {
+    return expandEvent;
+  }
+
+  void expandEvent(bool exp, var done) {
+    expand = exp;
+    done();
+  }
 }