Cleanup of various DOM dart2js and dart_analyzer warnings

tools/dom/src/WrappedList.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.
 
 part of dart.dom.html;
 
 /**
  * A list which just wraps another list, for either intercepting list calls or
  * retyping the list (for example, from List<A> to List<B> where B extends A).
  */
 class _WrappedList<E> extends ListBase<E> {
   final List _list;
 
   _WrappedList(this._list);
 
   // Iterable APIs
 
   Iterator<E> get iterator => new _WrappedIterator(_list.iterator);
 
   int get length => _list.length;
 
   // Collection APIs
 
   void add(E element) { _list.add(element); }
 
-  void remove(Object element) { _list.remove(element); }
+  bool remove(Object element) => _list.remove(element);
 
   void clear() { _list.clear(); }
 
   // List APIs
 
   E operator [](int index) => _list[index];
 
   void operator []=(int index, E value) { _list[index] = value; }
 
   void set length(int newLength) { _list.length = newLength; }
@@ skipping 30 matching lines @@
   Iterator _iterator;
 
   _WrappedIterator(this._iterator);
 
   bool moveNext() {
     return _iterator.moveNext();
   }
 
   E get current => _iterator.current;
 }