[layoutng] Implement state machine for async layout

third_party/WebKit/Source/core/layout/ng/ng_box_iterator.cc

-// Copyright 2016 The Chromium Authors. All rights reserved.
-// Use of this source code is governed by a BSD-style license that can be
-// found in the LICENSE file.
-
-#include "core/layout/ng/ng_box_iterator.h"
-#include "core/layout/ng/ng_box.h"
-
-namespace blink {
-
-NGBoxIterator::NGBoxIterator(NGBox box) : box_(box) {}
-
-NGBoxIterator::iterator& NGBoxIterator::iterator::operator=(
-    const NGBoxIterator::iterator& otherValue) {
-  box_ = otherValue.box_;
-  return (*this);
-}
-
-NGBoxIterator::iterator& NGBoxIterator::iterator::operator++() {
-  box_ = box_.nextSibling();
-  return (*this);
-}
-
-bool NGBoxIterator::iterator::operator!=(const iterator& other) {
-  return box_ != other.box_;
-}
-
-NGBox NGBoxIterator::iterator::operator*() {
-  return box_;
-}
-
-NGBoxIterator::iterator NGBoxIterator::begin() const {
-  return iterator(box_);
-}
-
-}  // namespace blink