Add refresh button to stack trace page.

runtime/bin/vmservice/client/lib/src/observatory_elements/stack_trace.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_trace_element;
 
+import 'dart:html';
 import 'observatory_element.dart';
 import 'package:polymer/polymer.dart';
 
 @CustomTag('stack-trace')
 class StackTraceElement extends ObservatoryElement {
   @published Map trace = toObservable({});
 
   StackTraceElement.created() : super.created();
-}
+
+  void refresh(Event e, var detail, Node target) {
+    var url = app.locationManager.currentIsolateRelativeLink('stacktrace');
+    app.requestManager.requestMap(url).then((map) {
+        trace = map;
+    }).catchError((e, trace) {
+        Logger.root.severe('Error while reloading stack trace: $e\n$trace');
+    });
+  }
+}