Revert of [LayoutNG] Move remaining ng_units structs to their own files

third_party/WebKit/Source/core/layout/ng/geometry/ng_margin_strut.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 NGMarginStrut_h
-#define NGMarginStrut_h
-
-#include "core/CoreExport.h"
-#include "platform/LayoutUnit.h"
-
-namespace blink {
-
-// This struct is used for the margin collapsing calculation.
-struct CORE_EXPORT NGMarginStrut {
-  LayoutUnit margin;
-  LayoutUnit negative_margin;
-
-  // Appends negative or positive value to the current margin strut.
-  void Append(const LayoutUnit& value);
-
-  // Sum up negative and positive margins of this strut.
-  LayoutUnit Sum() const;
-
-  bool operator==(const NGMarginStrut& other) const;
-
-  String ToString() const;
-};
-
-CORE_EXPORT std::ostream& operator<<(std::ostream&, const NGMarginStrut&);
-
-}  // namespace blink
-
-#endif  // NGMarginStrut_h