Implement a native identical function in the VM.

tests/language/identical_closure_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.
+
+var myIdentical = identical;
+
+class Point {
+  num x, y;
+  Point(this.x, this.y);
+}
+
+main() {
+  // Smi.
+  Expect.isTrue(myIdentical(42, 42));
+  Expect.isFalse(myIdentical(42, 41));
+
+  // Double.
+  Expect.isTrue(myIdentical(42.0, 42.0));
+  Expect.isFalse(myIdentical(42.0, 41.0));
+
+  // Mint.
+  Expect.isTrue(myIdentical(2.pow(45),2.pow(45)));
+  Expect.isFalse(myIdentical(2.pow(45),2.pow(45)+1));
+
+  // Bigint.
+  Expect.isTrue(myIdentical(-1*2.pow(76),-1*2.pow(76)));
+  Expect.isFalse(myIdentical(2.pow(76),2.pow(76)+1));
+
+  // Different types.
+  Expect.isFalse(myIdentical(42, 42.0));
+  Expect.isFalse(myIdentical("hello", 41));
+
+  // Points.
+  var p = new Point(1,1);
+  var q = new Point(1,1);
+  Expect.isFalse(myIdentical(p, q));
+
+  // Strings.
+  var a = "hello";
+  var b = "hello";
+  // Identical strings are coalesced into single instances.
+  Expect.isTrue(myIdentical(a, b));
+
+  // Null and NaN handling.
+  Expect.isFalse(myIdentical(42, null));
+  Expect.isTrue(myIdentical(null, null));
+  Expect.isTrue(myIdentical(double.NAN, double.NAN));
+}