Implement proposed new identity spec.

tests/language/number_identity2_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.
+// Dart test program for testing params.
+//
+// Contains test that is failing on dart2js. Merge this test with
+// 'number_identity_test.dart' once fixed.
+
+main() {
+  for (int i = 0; i < 1000; i++) testNumberIdentity();
+}
+
+
+testNumberIdentity () {
+  var a = double.NAN;
+  var b = a + 0.0;
+  Expect.isTrue(identical(a, b));
+}