[CSS Grid Layout] Implement auto-margin alignment for grid

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 150 matching lines @@
     bool canShrinkToFitInRowAxisForChild(const LayoutBox&) const;
     bool hasAutoMinSizeInRowAxis(const LayoutBox&) const;
     bool needToStretchChildLogicalHeight(const LayoutBox&) const;
     LayoutUnit childIntrinsicHeight(const LayoutBox&) const;
     LayoutUnit childIntrinsicWidth(const LayoutBox&) const;
     LayoutUnit intrinsicLogicalHeightForChild(const LayoutBox&) const;
     LayoutUnit marginLogicalHeightForChild(const LayoutBox&) const;
     LayoutUnit computeMarginLogicalHeightForChild(const LayoutBox&) const;
     LayoutUnit availableAlignmentSpaceForChildBeforeStretching(LayoutUnit gridAreaBreadthForChild, const LayoutBox&) const;
     void applyStretchAlignmentToChildIfNeeded(LayoutBox&);
+    bool hasAutoMarginsInColumnAxis(const LayoutBox&) const;
+    bool hasAutoMarginsInRowAxis(const LayoutBox&) const;
+    void resetAutoMarginsAndLogicalTopInColumnAxis(LayoutBox&);
+    void updateAutoMarginsInColumnAxisIfNeeded(LayoutBox&);
+    void updateAutoMarginsInRowAxisIfNeeded(LayoutBox&);
 
 #if ENABLE(ASSERT)
     bool tracksAreWiderThanMinTrackBreadth(GridTrackSizingDirection, const Vector<GridTrack>&);
 #endif
 
     size_t gridItemSpan(const LayoutBox&, GridTrackSizingDirection);
     bool spanningItemCrossesFlexibleSizedTracks(const GridCoordinate&, GridTrackSizingDirection) const;
 
     size_t gridColumnCount() const
     {
@@ skipping 17 matching lines @@
     OrderIterator m_orderIterator;
     Vector<LayoutBox*> m_gridItemsOverflowingGridArea;
     HashMap<const LayoutBox*, size_t> m_gridItemsIndexesMap;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutGrid, isLayoutGrid());
 
 } // namespace blink
 
 #endif // LayoutGrid_h