Make hasNext a getter instead of a method.

lib/coreimpl/hash_map_set.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.
 
 // Hash map implementation with open addressing and quadratic probing.
 class HashMapImplementation<K, V> implements HashMap<K, V> {
 
   // The [_keys] list contains the keys inserted in the map.
   // The [_keys] list must be a raw list because it
   // will contain both elements of type K, and the [_DELETED_KEY] of type
@@ skipping 388 matching lines @@
 
 class HashSetIterator<E> implements Iterator<E> {
 
   // TODO(4504458): Replace set_ with set.
   HashSetIterator(HashSetImplementation<E> set_)
     : _nextValidIndex = -1,
       _entries = set_._backingMap._keys {
     _advance();
   }
 
-  bool hasNext() {
+  bool get hasNext {
     if (_nextValidIndex >= _entries.length) return false;
     if (_entries[_nextValidIndex] === HashMapImplementation._DELETED_KEY) {
       // This happens in case the set was modified in the meantime.
       // A modification on the set may make this iterator misbehave,
       // but we should never return the sentinel.
       _advance();
     }
     return _nextValidIndex < _entries.length;
   }
 
   E next() {
-    if (!hasNext()) {
+    if (!hasNext) {
       throw const NoMoreElementsException();
     }
     E res = _entries[_nextValidIndex];
     _advance();
     return res;
   }
 
   void _advance() {
     int length = _entries.length;
     var entry;
@@ skipping 15 matching lines @@
 
 /**
  * A singleton sentinel used to represent when a key is deleted from the map.
  * We can't use [: const Object() :] as a sentinel because it would end up
  * canonicalized and then we cannot distinguish the deleted key from the
  * canonicalized [: Object() :].
  */
 class _DeletedKeySentinel {
   const _DeletedKeySentinel();
 }