Make hasNext a getter instead of a method.

tests/compiler/dart2js/mock_compiler.dart

Index: tests/compiler/dart2js/mock_compiler.dart
diff --git a/tests/compiler/dart2js/mock_compiler.dart b/tests/compiler/dart2js/mock_compiler.dart
index d2efbe062b1b8f1dadc6132fada43cfa0a58ef33..aab05cbc98c408fecdfd352d4619a4de7681af1c 100644
--- a/tests/compiler/dart2js/mock_compiler.dart
+++ b/tests/compiler/dart2js/mock_compiler.dart
@@ -202,19 +202,19 @@ void compareWarningKinds(String text, expectedWarnings, foundWarnings) {
   var fail = (message) => Expect.fail('$text: $message');
   Iterator<MessageKind> expected = expectedWarnings.iterator();
   Iterator<WarningMessage> found = foundWarnings.iterator();
-  while (expected.hasNext() && found.hasNext()) {
+  while (expected.hasNext && found.hasNext) {
     Expect.equals(expected.next(), found.next().message.kind);
   }
-  if (expected.hasNext()) {
+  if (expected.hasNext) {
     do {
       print('Expected warning "${expected.next()}" did not occur');
-    } while (expected.hasNext());
+    } while (expected.hasNext);
     fail('Too few warnings');
   }
-  if (found.hasNext()) {
+  if (found.hasNext) {
     do {
       print('Additional warning "${found.next()}"');
-    } while (found.hasNext());
+    } while (found.hasNext);
     fail('Too many warnings');
   }
 }