Fix all Observatory warnings/errors.

runtime/observatory/lib/src/elements/isolate_summary.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 isolate_summary_element;
 
-import 'dart:async';
 import 'observatory_element.dart';
 import 'package:observatory/app.dart';
 import 'package:observatory/service.dart';
 import 'package:polymer/polymer.dart';
 
 @CustomTag('isolate-summary')
 class IsolateSummaryElement extends ObservatoryElement {
   IsolateSummaryElement.created() : super.created();
 
   @published Isolate isolate;
@@ skipping 67 matching lines @@
     chart.update(counters);
     var element = shadowRoot.querySelector('#counterPieChart');
     if (element != null) {
       chart.draw(element);
     }
   }
 }