Converted Observatory cpu-profile element

runtime/observatory/lib/src/elements/class_tree.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 class_tree_element;
 
 import 'dart:html';
 import 'dart:async';
 import 'package:observatory/models.dart' as M;
 import 'package:observatory/src/elements/class_ref.dart';
@@ skipping 129 matching lines @@
       .expand((f) => f)
       ..forEach((subcls) {
         _mixins[subcls.id] = (_mixins[subcls.id] ?? [])..add(cls.mixin);
       });
   }
 
   static Element _create(toggle) {
     return new DivElement()..classes = ['class-tree-item']
         ..children = [
           new SpanElement()..classes = ['lines'],
-          new SpanElement()..classes = ['expander']
+          new ButtonElement()..classes = ['expander']
             ..onClick.listen((_) => toggle(autoToggleSingleChildNodes: true)),
           new SpanElement()..classes = ['name']
         ];
   }
 
   void _update(HtmlElement el, M.Class cls, int index) {
     virtualTreeUpdateLines(el.children[0], index);
     if (cls.subclasses.isEmpty) {
       el.children[1].text = '';
     } else {
@@ skipping 15 matching lines @@
           : new ClassRefElement(_isolate, type.typeClass, queue: _r.queue)
     ]).toList();
     children.first.text = ' with ';
     return children;
   }
 
   Iterable<M.Class> _children(M.Class cls) {
     return _subclasses[cls.id];
   }
 }