Don't restrict type on Setlet.remove.

dart/pkg/compiler/lib/src/util/setlet.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 dart2js.util.setlet;
 
 import 'dart:collection' show IterableBase;
 
 class Setlet<E> extends IterableBase<E> implements Set<E> {
   static const _MARKER = const _SetletMarker();
@@ skipping 139 matching lines @@
       for (int remaining = _extra, i = 0; remaining > 0 && i < CAPACITY; i++) {
         var candidate = _contents[i];
         if (_MARKER == candidate) continue;
         if (candidate == element) return candidate;
         remaining--;
       }
       return null;
     }
   }
 
-  bool remove(E element) {
+  bool remove(Object element) {
     if (_extra == null) {
       if (_contents == element) {
         _contents = _MARKER;
         return true;
       } else {
         return false;
       }
     } else if (_MARKER == _extra) {
       return _contents.remove(element);
     } else {
@@ skipping 132 matching lines @@
       if (Setlet._MARKER != candidate) {
         _current = candidate;
         _remaining--;
         return true;
       }
     }
     _current = null;
     return false;
   }
 }