Remove deprecated <, <=, >, and >= of DateTime.

tests/corelib/date_time6_test.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.
 
 import "package:expect/expect.dart";
 
 // Test DateTime comparison operators.
 
 main() {
   var d = new DateTime.fromMillisecondsSinceEpoch(0, isUtc: true);
   var d2 = new DateTime.fromMillisecondsSinceEpoch(1, isUtc: true);
-  Expect.isTrue(d < d2);
-  Expect.isTrue(d <= d2);
-  Expect.isTrue(d2 > d);
-  Expect.isTrue(d2 >= d);
-  Expect.isFalse(d2 < d);
-  Expect.isFalse(d2 <= d);
-  Expect.isFalse(d > d2);
-  Expect.isFalse(d >= d2);
+  Expect.isTrue(d.isBefore(d2));
+  Expect.isTrue(!d.isAfter(d2));
+  Expect.isTrue(d2.isAfter(d));
+  Expect.isTrue(!d2.isBefore(d));
+  Expect.isFalse(d2.isBefore(d));
+  Expect.isFalse(!d2.isAfter(d));
+  Expect.isFalse(d.isAfter(d2));
+  Expect.isFalse(!d.isBefore(d2));
 
   d = new DateTime.fromMillisecondsSinceEpoch(-1, isUtc: true);
   d2 = new DateTime.fromMillisecondsSinceEpoch(0, isUtc: true);
-  Expect.isTrue(d < d2);
-  Expect.isTrue(d <= d2);
-  Expect.isTrue(d2 > d);
-  Expect.isTrue(d2 >= d);
-  Expect.isFalse(d2 < d);
-  Expect.isFalse(d2 <= d);
-  Expect.isFalse(d > d2);
-  Expect.isFalse(d >= d2);
+  Expect.isTrue(d.isBefore(d2));
+  Expect.isTrue(!d.isAfter(d2));
+  Expect.isTrue(d2.isAfter(d));
+  Expect.isTrue(!d2.isBefore(d));
+  Expect.isFalse(d2.isBefore(d));
+  Expect.isFalse(!d2.isAfter(d));
+  Expect.isFalse(d.isAfter(d2));
+  Expect.isFalse(!d.isBefore(d2));
 }