[LayoutNG] Move remaining ng_units structs to their own files

third_party/WebKit/Source/core/layout/ng/geometry/ng_box_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 NGBoxStrut_h
+#define NGBoxStrut_h
+
+#include "core/CoreExport.h"
+#include "core/layout/ng/ng_writing_mode.h"

[mstensho (USE GERRIT), 2017/02/28 12:19:47]

Random thought (not something you necessarily need to address right now): Should
files in layout/ng/geometry/ really be allowed to access things in layout/ng/ ,
or should that be considered a layer violation?

[eae, 2017/02/28 12:26:34]

Ideally long term (post NG) all of these files should move to
Source/platform/geometry (and drop the ng prefix). As such writing mode should
be in  Source/platform and not in Source/core/layout/ng. For now though this is
probably fine. 

[mstensho (USE GERRIT), 2017/02/28 12:31:28]

Acknowledged.

Makes sense. Thanks.

+#include "platform/LayoutUnit.h"
+#include "platform/text/TextDirection.h"
+
+namespace blink {
+
+struct NGBoxStrut;
+
+// Struct to store physical dimensions, independent of writing mode and
+// direction.
+// See https://drafts.csswg.org/css-writing-modes-3/#abstract-box
+struct CORE_EXPORT NGPhysicalBoxStrut {
+  LayoutUnit left;
+  LayoutUnit right;
+  LayoutUnit top;
+  LayoutUnit bottom;
+  NGBoxStrut ConvertToLogical(NGWritingMode, TextDirection) const;
+};
+
+// This struct is used for storing margins, borders or padding of a box on all
+// four edges.
+struct CORE_EXPORT NGBoxStrut {
+  LayoutUnit inline_start;
+  LayoutUnit inline_end;
+  LayoutUnit block_start;
+  LayoutUnit block_end;
+
+  LayoutUnit InlineSum() const { return inline_start + inline_end; }
+  LayoutUnit BlockSum() const { return block_start + block_end; }
+
+  bool IsEmpty() const;
+
+  // The following two operators exist primarily to have an easy way to access
+  // the sum of border and padding.
+  NGBoxStrut& operator+=(const NGBoxStrut& other) {
+    inline_start += other.inline_start;
+    inline_end += other.inline_end;
+    block_start += other.block_start;
+    block_end += other.block_end;
+    return *this;
+  }
+
+  NGBoxStrut operator+(const NGBoxStrut& other) {
+    NGBoxStrut result(*this);
+    result += other;
+    return result;
+  }
+
+  bool operator==(const NGBoxStrut& other) const;
+
+  String ToString() const;
+};
+
+CORE_EXPORT std::ostream& operator<<(std::ostream&, const NGBoxStrut&);
+
+}  // namespace blink
+
+#endif  // NGBoxStrut_h