[LayoutNG] Remove unnecessary #inclusions of LayoutObject and derived class definitions.

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/layout_ng_block_flow.h"
 #include "core/layout/ng/ng_block_layout_algorithm.h"
 #include "core/layout/ng/ng_constraint_space.h"
 #include "core/layout/ng/ng_direction.h"
 #include "core/layout/ng/ng_fragment.h"
 #include "core/layout/ng/ng_fragment_builder.h"
 #include "core/layout/ng/ng_writing_mode.h"
-#include "core/layout/LayoutBlockFlow.h"
-#include "core/layout/LayoutBox.h"
 
 namespace blink {
 NGBox::NGBox(LayoutObject* layout_object)
     : layout_box_(toLayoutBox(layout_object)) {
   DCHECK(layout_box_);
 }
 
 NGBox::NGBox(ComputedStyle* style) : layout_box_(nullptr), style_(style) {
   DCHECK(style_);
 }
@@ skipping 104 matching lines @@
 
 bool NGBox::CanUseNewLayout() {
   if (!layout_box_)
     return true;
   if (!layout_box_->isLayoutBlockFlow())
     return false;
   const LayoutBlockFlow* block_flow = toLayoutBlockFlow(layout_box_);
   return !block_flow->childrenInline() || !block_flow->firstChild();
 }
 }  // namespace blink