[LayoutNG] Add NGLineBoxFragment

third_party/WebKit/Source/core/layout/ng/ng_line_height_metrics.h

+// Copyright 2017 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 NGLineHeightMetrics_h
+#define NGLineHeightMetrics_h
+
+#include "core/CoreExport.h"
+#include "core/layout/ng/ng_physical_fragment.h"
+#include "platform/fonts/FontBaseline.h"
+
+namespace blink {
+
+class ComputedStyle;
+class FontMetrics;
+
+// Represents line-progression metrics for line boxes and inline boxes.
+struct NGLineHeightMetrics {
+  NGLineHeightMetrics() {}
+
+  // Use the leading from the 'line-height' property, or the font metrics of
+  // the primary font if 'line-height: normal'.
+  NGLineHeightMetrics(const ComputedStyle&, FontBaseline);
+
+  // Use the leading from the font metrics.
+  NGLineHeightMetrics(const FontMetrics&, FontBaseline);
+
+  void Unite(const NGLineHeightMetrics&);
+
+  // TODO(kojii): Replace these floats with LayoutUnit.
+  float ascent = 0;
+  float descent = 0;
+  float ascent_and_leading = 0;
+  float descent_and_leading = 0;
+
+  LayoutUnit LineHeight() const {
+    return LayoutUnit(ascent_and_leading + descent_and_leading);
+  }
+
+ private:
+  void Initialize(const FontMetrics&, FontBaseline, float line_height);
+};
+
+}  // namespace blink
+
+#endif  // NGLineHeightMetrics_h