[es6] implement spread calls

src/harmony-spread.js

+// Copyright 2013 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.
+
+'use strict';
+
+// -------------------------------------------------------------------
+
+function SpreadArguments(a) {
+  // Each argument should be an array
+  var count = %_ArgumentsLength();
+  var array = (new InternalArray()).concat(%_Arguments(0));

[arv (Not doing code reviews), 2015/02/23 17:55:56]

Why not Push. concat creates a new array so we create one too many.

[rossberg, 2015/02/24 16:22:47]

+1, use push

+
+  for (var i = 1; i < count; ++i) {
+    array = array.concat(%_Arguments(i));

[arv (Not doing code reviews), 2015/02/23 17:55:56]

push here as well

or roll your own loop. It is usually faster but I'm not sure how much cruft
internal array push has.

+  }
+
+  return array;
+}
+
+function SpreadIterable(collection) {
+  if (IS_NULL_OR_UNDEFINED(collection)) {
+    throw MakeTypeError("not_iterable", [collection]);
+  }
+
+  var iterable = collection[symbolIterator];
+  var iterator = GetIterator(collection, iterable);

[arv (Not doing code reviews), 2015/02/23 17:55:56]

I'm on a mission to replace all of these with for-of since for-of will be able
to correctly handle the abrubt completion in the future so we don't have to
handle that all over the code base.

+  var args = new InternalArray();
+
+  while (true) {
+    var next = iterator.next();
+
+    if (!IS_OBJECT(next)) {
+      throw MakeTypeError("iterator_result_not_an_object", [next]);
+    }
+
+    if (next.done) {
+      break;
+    }
+
+    args.push(next.value);
+  }
+
+  return args;
+}