[CSS Grid Layout] Add support to place items using named grid lines

Source/core/rendering/RenderGrid.h

Index: Source/core/rendering/RenderGrid.h
diff --git a/Source/core/rendering/RenderGrid.h b/Source/core/rendering/RenderGrid.h
index d3fe920f6ac0b608d6fd5b95ec216d2150f66b15..ab65f6f4a5669547e651bc20dd643a1c1ac89600 100644
--- a/Source/core/rendering/RenderGrid.h
+++ b/Source/core/rendering/RenderGrid.h
@@ -35,10 +35,7 @@ struct GridCoordinate;
 struct GridSpan;
 class GridTrack;
 
-enum GridTrackSizingDirection {
-    ForColumns,
-    ForRows
-};
+typedef HashMap<String, Vector<size_t> > NamedGridLinesMap;
 
 class RenderGrid FINAL : public RenderBlock {
 public:
@@ -153,6 +150,9 @@ private:
         return m_grid.size();
     }
 
+    const NamedGridLinesMap& gridLinesForSide(GridPositionSide side) const { return (side == ColumnStartSide || side == ColumnEndSide) ? m_namedGridColumnLines : m_namedGridRowLines; }
+    void createGridLineNamesMapsForDirection(GridTrackSizingDirection);
+
     typedef Vector<RenderBox*, 1> GridCell;
     typedef Vector<Vector<GridCell> > GridRepresentation;
     GridRepresentation m_grid;
@@ -163,6 +163,9 @@ private:
     OrderIterator m_orderIterator;
     Vector<RenderBox*> m_gridItemsOverflowingGridArea;
 
+    NamedGridLinesMap m_namedGridColumnLines;
+    NamedGridLinesMap m_namedGridRowLines;
+
     friend class GridCoordinateSorter;
 };