Make dart:collection strong-mode clean.

sdk/lib/collection/iterator.dart

 // Copyright (c) 2012, 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.collection;
 
 /**
  * The [HasNextIterator] class wraps an [Iterator] and provides methods to
  * iterate over an object using `hasNext` and `next`.
  *
  * An [HasNextIterator] does not implement the [Iterator] interface.
  */
 class HasNextIterator<E> {
   static const int _HAS_NEXT_AND_NEXT_IN_CURRENT = 0;
   static const int _NO_NEXT = 1;
   static const int _NOT_MOVED_YET = 2;
 
-  Iterator _iterator;
+  Iterator<E> _iterator;
   int _state = _NOT_MOVED_YET;
 
   HasNextIterator(this._iterator);
 
   bool get hasNext {
     if (_state == _NOT_MOVED_YET) _move();
     return _state == _HAS_NEXT_AND_NEXT_IN_CURRENT;
   }
 
   E next() {
     // Call to hasNext is necessary to make sure we are positioned at the first
     // element when we start iterating.
     if (!hasNext) throw new StateError("No more elements");
     assert(_state == _HAS_NEXT_AND_NEXT_IN_CURRENT);
     E result = _iterator.current;
     _move();
     return result;
   }
 
   void _move() {
     if (_iterator.moveNext()) {
       _state = _HAS_NEXT_AND_NEXT_IN_CURRENT;
     } else {
       _state = _NO_NEXT;
     }
   }
 }