[LayoutNG] Move remaining ng_units structs to their own files

third_party/WebKit/Source/core/layout/ng/geometry/ng_margin_strut.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/geometry/ng_margin_strut.h"
+
+#include "wtf/text/WTFString.h"
+
+namespace blink {
+
+LayoutUnit NGMarginStrut::Sum() const {
+  return margin + negative_margin;
+}
+
+bool NGMarginStrut::operator==(const NGMarginStrut& other) const {
+  return margin == other.margin && negative_margin == other.negative_margin;
+}
+
+void NGMarginStrut::Append(const LayoutUnit& value) {
+  if (value < 0) {
+    negative_margin = std::min(value, negative_margin);
+  } else {
+    margin = std::max(value, margin);
+  }
+}
+
+String NGMarginStrut::ToString() const {
+  return String::format("%d %d", margin.toInt(), negative_margin.toInt());
+}
+
+std::ostream& operator<<(std::ostream& stream, const NGMarginStrut& value) {
+  return stream << value.ToString();
+}
+
+}  // namespace blink