Move builtin JavaScript sources into own directory.

src/harmony-spread.js

-// 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.
-
-(function(global, utils) {
-
-'use strict';
-
-// -------------------------------------------------------------------
-// Imports
-var InternalArray = utils.InternalArray;
-
-// -------------------------------------------------------------------
-
-function SpreadArguments() {
-  var count = %_ArgumentsLength();
-  var args = new InternalArray();
-
-  for (var i = 0; i < count; ++i) {
-    var array = %_Arguments(i);
-    var length = array.length;
-    for (var j = 0; j < length; ++j) {
-      args.push(array[j]);
-    }
-  }
-
-  return args;
-}
-
-
-function SpreadIterable(collection) {
-  if (IS_NULL_OR_UNDEFINED(collection)) {
-    throw MakeTypeError(kNotIterable, collection);
-  }
-
-  var args = new InternalArray();
-  for (var value of collection) {
-    args.push(value);
-  }
-  return args;
-}
-
-// ----------------------------------------------------------------------------
-// Exports
-
-%InstallToContext([
-  "spread_arguments", SpreadArguments,
-  "spread_iterable", SpreadIterable,
-]);
-
-})