Implement a native identical function in the VM.

runtime/lib/identical_patch.dart

Index: runtime/lib/identical_patch.dart
diff --git a/runtime/lib/identical_patch.dart b/runtime/lib/identical_patch.dart
index 218b3c83f1b46bb2988ee1f2b6f4b3185072ec17..b7f8f188cd71316aef1c2a8b02823c5c983f7b91 100644
--- a/runtime/lib/identical_patch.dart
+++ b/runtime/lib/identical_patch.dart
@@ -2,6 +2,4 @@
 // 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.
 
-patch bool identical(Object a, Object b) {
-  throw new Error('Should not reach the body of identical');  
-}
+patch bool identical(Object a, Object b) native "Identical_comparison";