Add corelib tests

test/codegen/corelib/null_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 that Null inherits properties from Object.
+
+main() {
+  var x;
+
+  Expect.isTrue(x is Object);
+  Expect.isTrue(x is dynamic);
+  Expect.isTrue(x is! String);
+  Expect.isTrue(x is! int);
+
+  // These shouldn't throw.
+  x.runtimeType;
+  x.toString();
+  x.hashCode;
+
+  // operator== is inherited from Object. It's the same as identical.
+  // It's not really testable.
+  Expect.isTrue(identical(x, null));
+  Expect.isTrue(x == null);
+
+  // Methods can be closurized and yields the same result.
+  var ts = x.toString;
+  Expect.equals(null.toString(), ts());
+
+  // noSuchMethod is tested in null_nosuchmethod_test.dart.
+}