Build Observatory as part of runtime

runtime/observatory/lib/src/elements/sliding_checkbox.dart

 // Copyright (c) 2014, 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 sliding_checkbox_element;
 
 import 'dart:html';
 import 'package:polymer/polymer.dart';
 
 @CustomTag('sliding-checkbox')
 class SlidingCheckboxElement extends PolymerElement {
   SlidingCheckboxElement.created() : super.created();
   @published bool checked;
   @published String checkedText;
   @published String uncheckedText;
 
   void change(Event e, var details, Node target) {
     CheckboxInputElement input = shadowRoot.querySelector('#slide-switch');
     checked = input.checked;
   }
 }