Make hasNext a getter instead of a method.

tests/compiler/dart2js/gvn_test.dart

 // Copyright (c) 2011, 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.
 
 #import("compiler_helper.dart");
 
 const String TEST_ONE = r"""
 void foo(bar) {
   for (int i = 0; i < 1; i++) {
     print(1 + bar);
     print(1 + bar);
   }
 }
 """;
 
 main() {
   String generated = compile(TEST_ONE, entry: 'foo');
   RegExp regexp = const RegExp(r"1 \+ [a-z]+");
   Iterator matches = regexp.allMatches(generated).iterator();
-  Expect.isTrue(matches.hasNext());
+  Expect.isTrue(matches.hasNext);
   matches.next();
-  Expect.isFalse(matches.hasNext());
+  Expect.isFalse(matches.hasNext);
 }