[LayoutNG] Initial support for the 'vertical-align' property

third_party/WebKit/Source/core/layout/ng/inline/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.
 // Computed for inline boxes, then the metrics of inline boxes are united to
 // compute metrics for line boxes.
 // https://drafts.csswg.org/css2/visudet.html#line-height
 struct NGLineHeightMetrics {
-  NGLineHeightMetrics() {}
+  NGLineHeightMetrics()
+      : ascent(LayoutUnit::Min()), descent(LayoutUnit::Min()) {}
   NGLineHeightMetrics(LayoutUnit initial_ascent, LayoutUnit initial_descent)
       : ascent(initial_ascent), descent(initial_descent) {}
 
   // Compute from ComputedStyle, using the font metrics of the prikmary font.
   // The leading is not included.
   NGLineHeightMetrics(const ComputedStyle&, FontBaseline);
 
   // Compute from FontMetrics. The leading is not included.
   NGLineHeightMetrics(const FontMetrics&, FontBaseline);
 
+  bool IsEmpty() const { return ascent == LayoutUnit::Min(); }
+
   // Add the leading. Half the leading is added to ascent and descent each.
   // https://drafts.csswg.org/css2/visudet.html#leading
   void AddLeading(LayoutUnit line_height);
 
+  // Move the metrics by the specified amount, in line progression direction.
+  void Move(LayoutUnit);
+
   // Unite a metrics for an inline box to a metrics for a line box.
   void Unite(const NGLineHeightMetrics&);
 
   // Ascent and descent of glyphs, or synthesized for replaced elements.
   // Then united to compute 'text-top' and 'text-bottom' of line boxes.
   LayoutUnit ascent;
   LayoutUnit descent;
 
   LayoutUnit LineHeight() const { return ascent + descent; }
 
  private:
   void Initialize(const FontMetrics&, FontBaseline);
 };
 
 }  // namespace blink
 
 #endif  // NGLineHeightMetrics_h