Implement proposed new identity spec.

tests/standalone/number_identity_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.
+//
+// Tests 'identical' for cases that not supported in dart2js (bigint,
+// disambiguation int/double).
+
+main() {
+  for (int i = 0; i < 1000; i++) testNumberIdentity();
+}
+
+
+testNumberIdentity () {
+  const int smi = 8;
+  const int bigint = 22107138293752210713829375;
+  const double dbl = 8.0;
+  // No int/double differences in dart2js.
+  var a = smi + 0;
+  Expect.isFalse(identical(a, dbl));
+  a = dbl + 0.0;
+  Expect.isFalse(identical(a, smi));
+
+  a = bigint;
+  var b = a + 0;
+  Expect.isTrue(identical(a, b));
+  b = a + 1;
+  Expect.isFalse(identical(a, b));  // Fails with dart2js.
+}