array-iterator.js: use object_get_prototype_of instead of directly accessing the proto

Instead of directly looking up Uint8Array.__proto__, to get a hold of
the TypedArray prototype, use object_get_prototype_of. This is a
functionally equivalent, but cleaner approach.

Review-Url: https://codereview.chromium.org/1990983002
Cr-Commit-Position: refs/heads/master@{#36340}

src/js/array-iterator.js

@@ -22,7 +22,7 @@ var IteratorPrototype = utils.ImportNow("IteratorPrototype");
 var iteratorSymbol = utils.ImportNow("iterator_symbol");
 var MakeTypeError;
 var toStringTagSymbol = utils.ImportNow("to_string_tag_symbol");
-var GlobalTypedArray = global.Uint8Array.__proto__;
+var GlobalTypedArray = %object_get_prototype_of(global.Uint8Array);
 
 utils.Import(function(from) {
   MakeTypeError = from.MakeTypeError;