[css-grid] Implementing the grid's first line baseline.

third_party/WebKit/Source/core/layout/LayoutGrid.h

 /*
  * Copyright (C) 2011 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
  *    notice, this list of conditions and the following disclaimer in the
@@ skipping 281 matching lines @@
            hasAutoSizeInColumnAxis(child) && !hasAutoMarginsInColumnAxis(child);
   }
   bool allowedToStretchChildAlongRowAxis(const LayoutBox& child) const {
     return justifySelfForChild(child).position() == ItemPositionStretch &&
            hasAutoSizeInRowAxis(child) && !hasAutoMarginsInRowAxis(child);
   }
   bool hasAutoMarginsInColumnAxis(const LayoutBox&) const;
   bool hasAutoMarginsInRowAxis(const LayoutBox&) const;
   void updateAutoMarginsInColumnAxisIfNeeded(LayoutBox&);
   void updateAutoMarginsInRowAxisIfNeeded(LayoutBox&);
+  LayoutUnit firstLineBoxBaselineForChild(const LayoutBox&) const;
+
+  int baselinePosition(
+      FontBaseline,
+      bool firstLine,
+      LineDirectionMode,
+      LinePositionMode = PositionOnContainingLine) const override;
+  int firstLineBoxBaseline() const override;
+  int inlineBlockBaseline(LineDirectionMode) const override;
 
 #if ENABLE(ASSERT)
   bool tracksAreWiderThanMinTrackBreadth(GridTrackSizingDirection,
                                          GridSizingData&) const;
 #endif
 
   LayoutUnit gridGapForDirection(GridTrackSizingDirection,
                                  SizingOperation) const;
   LayoutUnit guttersSize(GridTrackSizingDirection,
                          size_t startLine,
@@ skipping 42 matching lines @@
   std::unique_ptr<OrderedTrackIndexSet> m_autoRepeatEmptyRows{nullptr};
 
   Optional<bool> m_hasDefiniteLogicalHeight;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutGrid, isLayoutGrid());
 
 }  // namespace blink
 
 #endif  // LayoutGrid_h