[LayoutNG] Initial implementation of NGBoxIterator

third_party/WebKit/Source/core/layout/ng/ng_block_layout_algorithm.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_block_layout_algorithm.h"
 
 #include "core/layout/LayoutBox.h"
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_fragment.h"
 #include "core/layout/ng/ng_length_utils.h"
 #include "core/style/ComputedStyle.h"
 #include "platform/LengthFunctions.h"
 
 namespace blink {
 
 NGBlockLayoutAlgorithm::NGBlockLayoutAlgorithm(
     PassRefPtr<const ComputedStyle> style,
-    NGBox firstChild)
-    : m_style(style), m_firstChild(firstChild) {}
+    NGBoxIterator boxIterator)
+    : m_style(style), m_boxIterator(boxIterator) {}
 
 NGFragment* NGBlockLayoutAlgorithm::layout(
     const NGConstraintSpace& constraintSpace) {
   LayoutUnit inlineSize =
       computeInlineSizeForFragment(constraintSpace, *m_style);
 
   HeapVector<Member<const NGFragmentBase>> childFragments;
-
   LayoutUnit contentSize;
-  for (NGBox curr = m_firstChild; curr; curr.nextSibling()) {
+  for (NGBox curr = m_boxIterator.first(); curr; m_boxIterator.next()) {
     NGFragment* fragment = curr.layout(constraintSpace);
     // TODO(layout-ng): Take margins into account
     fragment->setOffset(LayoutUnit(), contentSize);
     contentSize += fragment->blockSize();
     childFragments.append(fragment);
   }
 
   LayoutUnit blockSize =
       computeBlockSizeForFragment(constraintSpace, *m_style, contentSize);
   NGFragment* returnFragment = new NGFragment(
       inlineSize, blockSize, inlineSize, blockSize,
       NGFragmentBase::HorizontalTopBottom, NGFragmentBase::LeftToRight);
   returnFragment->swapChildren(childFragments);
   return returnFragment;
 }
 
 }  // namespace blink