Revert of [LayoutNG] Initial implementation of NGBoxIterator

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(const LayoutObject* layoutObject)
-    : m_layoutObject(layoutObject), m_currentChild(nullptr) {}
-
-NGBox NGBoxIterator::first() {
-  reset();
-  return next();
-}
-
-NGBox NGBoxIterator::next() {
-  if (!m_currentChild) {
-    m_currentChild = m_layoutObject->slowFirstChild();
-  } else {
-    m_currentChild = m_layoutObject->nextSibling();
-  }
-  return NGBox(m_currentChild);
-}
-
-void NGBoxIterator::reset() {
-  m_currentChild = nullptr;
-}
-
-}  // namespace blink