Fix ContainerTypeMask== and ContainerTypeMask.hashCode.

tests/compiler/dart2js/container_mask_equal_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.
+
+// Regression test for dart2js that used to have a bogus
+// implementation of var.== and
+// var.hashCode. 
+
+import 'package:expect/expect.dart';
+import "package:async_helper/async_helper.dart";
+import 'memory_compiler.dart';
+
+const MEMORY_SOURCE_FILES = const {
+  'main.dart': '''
+
+import 'dart:typed_data';
+
+a() => [0];
+b() => [1, 2];
+c() => new Uint8List(1);
+d() => new Uint8List(2);
+
+main() {
+  print(a); print(b); print(c); print(d);
+}
+''',
+};
+
+main() {
+  var compiler = compilerFor(MEMORY_SOURCE_FILES);  
+  asyncTest(() => compiler.run(Uri.parse('memory:main.dart')).then((_) {
+    var typesInferrer = compiler.typesTask.typesInferrer;
+
+    var element = compiler.mainApp.find('a');
+    var mask1 = typesInferrer.getReturnTypeOfElement(element);
+
+    element = compiler.mainApp.find('b');
+    var mask2 = typesInferrer.getReturnTypeOfElement(element);
+
+    element = compiler.mainApp.find('c');
+    var mask3 = typesInferrer.getReturnTypeOfElement(element);
+
+    element = compiler.mainApp.find('d');
+    var mask4 = typesInferrer.getReturnTypeOfElement(element);
+
+    Expect.notEquals(mask1.union(mask2, compiler),
+                     mask3.union(mask4, compiler));
+  }));
+}