Add shift to InternalArray and InternalPackedArray

src/array.js

Index: src/array.js
diff --git a/src/array.js b/src/array.js
index e0a1fc98a655053c42e5dbadcb19032d5210e237..db364be84bbcd1b5146b8667983e2d7086419e7c 100644
--- a/src/array.js
+++ b/src/array.js
@@ -1579,13 +1579,15 @@ SetUpLockedPrototype(InternalArray, GlobalArray(), [
   "join", getFunction("join", ArrayJoin),
   "pop", getFunction("pop", ArrayPop),
   "push", getFunction("push", ArrayPush),
+  "shift", getFunction("shift", ArrayShift),
   "splice", getFunction("splice", ArraySplice)
 ]);
 
 SetUpLockedPrototype(InternalPackedArray, GlobalArray(), [
   "join", getFunction("join", ArrayJoin),
   "pop", getFunction("pop", ArrayPop),
-  "push", getFunction("push", ArrayPush)
+  "push", getFunction("push", ArrayPush),
+  "shift", getFunction("shift", ArrayShift)
 ]);
 
 $arrayConcat = ArrayConcatJS;