[layoutng] Implement state machine for async layout

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

-// 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.
-
-#ifndef NGBoxIterator_h
-#define NGBoxIterator_h
-
-#include "core/layout/LayoutObject.h"
-#include "core/layout/ng/ng_box.h"
-
-namespace blink {
-
-class NGBox;
-
-// NG Box iterator over siblings of the layout object.
-class CORE_EXPORT NGBoxIterator
-    : public std::iterator<std::forward_iterator_tag, NGBox> {
- public:
-  class iterator {
-   public:
-    iterator& operator=(const iterator& otherValue);
-    iterator(NGBox box) : box_(box) {}
-    iterator& operator++();
-    bool operator!=(const iterator& other);
-    NGBox operator*();
-
-   private:
-    NGBox box_;
-  };
-  explicit NGBoxIterator(NGBox);
-
-  iterator begin() const;
-  iterator end() const { return iterator(NGBox()); }
-
- private:
-  NGBox box_;
-};
-
-}  // namespace blink
-#endif  // NGBoxIterator_h