Disallow subclassing Arrays.

src/messages.js

Index: src/messages.js
diff --git a/src/messages.js b/src/messages.js
index 19cc6edc5500ce4301cdfc9c5ba096a0f0a8c164..37182414ec11802a939030e7cfe75f1a5e1d8df2 100644
--- a/src/messages.js
+++ b/src/messages.js
@@ -187,7 +187,8 @@ var kMessages = {
   super_constructor_call:        ["A 'super' constructor call may only appear as the first statement of a function, and its arguments may not access 'this'. Other forms are not yet supported."],
   duplicate_proto:               ["Duplicate __proto__ fields are not allowed in object literals"],
   param_after_rest:              ["Rest parameter must be last formal parameter"],
-  constructor_noncallable:       ["Class constructors cannot be invoked without 'new'"]
+  constructor_noncallable:       ["Class constructors cannot be invoked without 'new'"],
+  array_not_subclassable:        ["Subclassing Arrays is not currently supported."]
 };