[LayoutNG] Add NGLineBoxFragment

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

+// 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.
+
+#include "core/layout/ng/ng_line_height_metrics.h"
+
+#include "core/style/ComputedStyle.h"
+
+namespace blink {
+
+NGLineHeightMetrics::NGLineHeightMetrics(const ComputedStyle& style,
+                                         FontBaseline baseline_type) {
+  const SimpleFontData* font_data = style.font().primaryFont();
+  DCHECK(font_data);
+  Initialize(font_data->getFontMetrics(), baseline_type,
+             style.computedLineHeightInFloat());
+}
+
+NGLineHeightMetrics::NGLineHeightMetrics(const FontMetrics& font_metrics,
+                                         FontBaseline baseline_type) {
+  Initialize(font_metrics, baseline_type, font_metrics.floatLineSpacing());
+}
+
+void NGLineHeightMetrics::Initialize(const FontMetrics& font_metrics,
+                                     FontBaseline baseline_type,
+                                     float line_height) {
+  ascent = font_metrics.floatAscent(baseline_type);
+  descent = font_metrics.floatDescent(baseline_type);
+  float half_leading = (line_height - (ascent + descent)) / 2;
+  // Ensure the top and the baseline is snapped to CSS pixel.
+  // TODO(kojii): How to handle fractional ascent isn't determined yet. Should
+  // we snap top or baseline? If baseline, top needs fractional. If top,
+  // baseline may not align across fonts.
+  ascent_and_leading = ascent + floor(half_leading);
+  descent_and_leading = line_height - ascent_and_leading;
+}
+
+void NGLineHeightMetrics::Unite(const NGLineHeightMetrics& other) {
+  ascent = std::max(ascent, other.ascent);
+  descent = std::max(descent, other.descent);
+  ascent_and_leading = std::max(ascent_and_leading, other.ascent_and_leading);
+  descent_and_leading =
+      std::max(descent_and_leading, other.descent_and_leading);
+}
+
+}  // namespace blink