Make isEmpty a getter.

lib/core/expect.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.
 
 /**
  * Expect is used for tests that do not want to make use of the
  * Dart unit test library - for example, the core language tests.
  * Third parties are discouraged from using this, and should use
  * the expect() function in the unit test library instead for
  * test assertions.
@@ skipping 209 matching lines @@
    * every element of [actual] is also in [expected].
    */
   static void setEquals(Iterable expected,
                         Iterable actual,
                         [String reason = null]) {
     final missingSet = new Set.from(expected);
     missingSet.removeAll(actual);
     final extraSet = new Set.from(actual);
     extraSet.removeAll(expected);
 
-    if (extraSet.isEmpty() && missingSet.isEmpty()) return;
+    if (extraSet.isEmpty && missingSet.isEmpty) return;
     String msg = _getMessage(reason);
 
     StringBuffer sb = new StringBuffer("Expect.setEquals($msg) fails");
     // Report any missing items.
-    if (!missingSet.isEmpty()) {
+    if (!missingSet.isEmpty) {
       sb.add('\nExpected collection does not contain: ');
     }
 
     for (final val in missingSet) {
       sb.add('$val ');
     }
 
     // Report any extra items.
-    if (!extraSet.isEmpty()) {
+    if (!extraSet.isEmpty) {
       sb.add('\nExpected collection should not contain: ');
     }
 
     for (final val in extraSet) {
       sb.add('$val ');
     }
     _fail(sb.toString());
   }
 
   /**
@@ skipping 27 matching lines @@
   }
 }
 
 typedef bool _CheckExceptionFn(exception);
 
 class ExpectException implements Exception {
   ExpectException(this.message);
   String toString() => message;
   String message;
 }