Introduce InternalPackedArray.

src/array.js

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 1541 matching lines @@
   // The internal Array prototype doesn't need to be fancy, since it's never
   // exposed to user code.
   // Adding only the functions that are actually used.
   SetUpLockedPrototype(InternalArray, $Array(), $Array(
     "indexOf", getFunction("indexOf", ArrayIndexOf),
     "join", getFunction("join", ArrayJoin),
     "pop", getFunction("pop", ArrayPop),
     "push", getFunction("push", ArrayPush),
     "splice", getFunction("splice", ArraySplice)
   ));
+
+  SetUpLockedPrototype(InternalPackedArray, $Array(), $Array(
+    "join", getFunction("join", ArrayJoin),
+    "pop", getFunction("pop", ArrayPop),
+    "push", getFunction("push", ArrayPush)
+  ));
 }
 
 SetUpArray();