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

Source/core/rendering/style/GridCoordinate.h

Index: Source/core/rendering/style/GridCoordinate.h
diff --git a/Source/core/rendering/style/GridCoordinate.h b/Source/core/rendering/style/GridCoordinate.h
index 1e3421ec370b71ad60d301a4eea450a521b788e8..462241a16b0afb88292b3f9f152d77222e555398 100644
--- a/Source/core/rendering/style/GridCoordinate.h
+++ b/Source/core/rendering/style/GridCoordinate.h
@@ -143,12 +143,33 @@ struct GridCoordinate {
         return !(*this == o);
     }
 
+    size_t positionForSide(GridPositionSide side) const
+    {
+        switch (side) {
+        case ColumnStartSide:
+            return columns.initialPositionIndex;
+        case ColumnEndSide:
+            return columns.finalPositionIndex;
+        case RowStartSide:
+            return rows.initialPositionIndex;
+        case RowEndSide:
+            return rows.finalPositionIndex;
+        }
+        ASSERT_NOT_REACHED();
+        return 0;
+    }
+
     GridSpan columns;
     GridSpan rows;
 };
 
 typedef HashMap<String, GridCoordinate> NamedGridAreaMap;
 
+enum GridTrackSizingDirection {
+    ForColumns,
+    ForRows
+};
+
 } // namespace WebCore
 
 #endif // GridCoordinate_h