[LayoutNG] Initial implementation of NGBoxIterator

third_party/WebKit/Source/core/layout/ng/ng_box.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.h"
 
 #include "core/layout/LayoutObject.h"
 #include "core/layout/ng/ng_block_layout_algorithm.h"
 
 namespace blink {
 
 NGFragment* NGBox::layout(const NGConstraintSpace& constraintSpace) {
-  NGBlockLayoutAlgorithm algorithm(style(), firstChild());
+  NGBlockLayoutAlgorithm algorithm(style(), iterator());
   return algorithm.layout(constraintSpace);
 }
 
 const ComputedStyle* NGBox::style() const {
   return m_layoutObject->style();
 }
 
-const NGBox NGBox::firstChild() const {
-  return NGBox(m_layoutObject->slowFirstChild());
-}
-
-const NGBox NGBox::nextSibling() const {
-  return NGBox(m_layoutObject->nextSibling());
-}
-
 }  // namespace blink