Fixing analyzer warnings on overloading == but not get hashCode.

tests/html/rect_test.dart

 // Copyright (c) 2013, 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.
 
 library rect_test;
 
 import 'dart:html';
 import '../../pkg/unittest/lib/unittest.dart';
 import '../../pkg/unittest/lib/html_config.dart';
 
@@ skipping 129 matching lines @@
   test('toInt', () {
     var rect = new Rect(11.4, 26.6, 17.8, 9.2);
     var b = rect.toInt();
     expect(b, new Rect(11, 26, 17, 9));
 
     expect(b.left is int, isTrue);
     expect(b.top is int, isTrue);
     expect(b.width is int, isTrue);
     expect(b.height is int, isTrue);
   });
+
+  test('hashCode', () {
+    var a = new Rect(0, 1, 2, 3);
+    var b = new Rect(0, 1, 2, 3);
+    expect(a.hashCode, b.hashCode);
+
+    var c = new Rect(1, 0, 2, 3);
+    expect(a.hashCode == c.hashCode, isFalse);
+  });
 }