Move builtin JavaScript sources into own directory.

src/iterator-prototype.js

Index: src/iterator-prototype.js
diff --git a/src/iterator-prototype.js b/src/iterator-prototype.js
deleted file mode 100644
index 2f49d90b1c97baa9fd39723f5e559e426843bc07..0000000000000000000000000000000000000000
--- a/src/iterator-prototype.js
+++ /dev/null
@@ -1,22 +0,0 @@
-// Copyright 2015 the V8 project authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-var $iteratorPrototype;
-
-(function(global, utils) {
-  "use strict";
-  %CheckIsBootstrapping();
-
-  var GlobalObject = global.Object;
-  var iteratorSymbol = utils.ImportNow("iterator_symbol");
-
-  // 25.1.2.1 %IteratorPrototype% [ @@iterator ] ( )
-  function IteratorPrototypeIterator() {
-    return this;
-  }
-
-  utils.SetFunctionName(IteratorPrototypeIterator, iteratorSymbol);
-  %AddNamedProperty($iteratorPrototype, iteratorSymbol,
-      IteratorPrototypeIterator, DONT_ENUM);
-})