fix webui for sdk 0.8.7

lib/observe/set.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 web_ui.observe.set;
 
 import 'dart:collection';
 import 'observable.dart';
 import 'map.dart' show MapFactory;
 import 'package:web_ui/src/utils_observe.dart' show IterableWorkaround;
@@ skipping 35 matching lines @@
    */
   bool contains(E value) {
     if (observeReads) notifyRead(this, ChangeRecord.INDEX, value);
     return _map.containsKey(value);
   }
 
   /**
    * Adds [value] into the set. The method has no effect if
    * [value] was already in the set.
    */
-  void add(E value) {
+  bool add(E value) {
     int len = _map.length;
     _map[value] = const Object();
     if (len != _map.length) {
       notifyChange(this, ChangeRecord.FIELD, 'length', len, _map.length);
       notifyChange(this, ChangeRecord.INSERT, value, null, value);
+      return true;
     }
+    return false;
   }
 
   /**
    * Removes [value] from the set. Returns true if [value] was
    * in the set. Returns false otherwise. The method has no effect
    * if [value] value was not in the set.
    */
   bool remove(E value) {
     // notifyRead because result depends on if the key already exists
     if (observeReads) notifyRead(this, ChangeRecord.INDEX, value);
@@ skipping 30 matching lines @@
 
   bool get isEmpty => length == 0;
 
   Iterator<E> get iterator => new _ObservableSetIterator<E>(this);
 
   /**
    * Adds all the elements of the given collection to the set.
    */
   void addAll(Iterable<E> collection) => collection.forEach(add);
 
+  E lookup(Object object) { throw new UnimplementedError(); }
+
   /**
    * Removes all the elements of the given collection from the set.
    */
   void removeAll(Iterable collection) => collection.forEach(remove);
 
   void retainAll(Iterable collection) => retainWhere(collection.contains);
 
   void removeWhere(bool test(E element)) =>
       where(test).toList().forEach(remove);
 
@@ skipping 57 matching lines @@
     _set.length;
     return _hasNext = _iterator.moveNext();
   }
 
   E get current {
     var result = _iterator.current;
     if (observeReads && _hasNext) notifyRead(_set, ChangeRecord.INDEX, result);
     return result;
   }
 }