[CSS Grid Layout] Speed up painting on large grids

Source/core/rendering/RenderGrid.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 73 matching lines @@
     void insertItemIntoGrid(RenderBox*, const GridCoordinate&);
     void placeItemsOnGrid();
     void populateExplicitGridAndOrderIterator();
     void placeSpecifiedMajorAxisItemsOnGrid(Vector<RenderBox*>);
     void placeAutoMajorAxisItemsOnGrid(Vector<RenderBox*>);
     void placeAutoMajorAxisItemOnGrid(RenderBox*);
     TrackSizingDirection autoPlacementMajorAxisDirection() const;
     TrackSizingDirection autoPlacementMinorAxisDirection() const;
 
     void layoutGridItems();
+    void populateGridPositions(const Vector<GridTrack>& columnTracks, const Vector<GridTrack>& rowTracks);
 
     virtual bool supportsPartialLayout() const OVERRIDE { return false; }
 
     typedef LayoutUnit (RenderGrid::* SizingFunction)(RenderBox*, TrackSizingDirection, Vector<GridTrack>&);
     typedef LayoutUnit (GridTrack::* AccumulatorGetter)() const;
     typedef void (GridTrack::* AccumulatorGrowFunction)(LayoutUnit);
     typedef bool (GridTrackSize::* FilterFunction)() const;
     void resolveContentBasedTrackSizingFunctionsForItems(TrackSizingDirection, Vector<GridTrack>& columnTracks, Vector<GridTrack>& rowTracks, RenderBox*, FilterFunction, SizingFunction, AccumulatorGetter, AccumulatorGrowFunction);
     void distributeSpaceToTracks(Vector<GridTrack*>&, Vector<GridTrack*>* tracksForGrowthAboveMaxBreadth, AccumulatorGetter, AccumulatorGrowFunction, LayoutUnit& availableLogicalSpace);
 
@@ skipping 37 matching lines @@
     size_t gridRowCount() const
     {
         ASSERT(!gridIsDirty());
         return m_grid.size();
     }
 
     typedef Vector<RenderBox*, 1> GridCell;
     typedef Vector<Vector<GridCell> > GridRepresentation;
     GridRepresentation m_grid;
     bool m_gridIsDirty;
+    Vector<LayoutUnit> m_rowPositions;
+    Vector<LayoutUnit> m_columnPositions;
     HashMap<const RenderBox*, GridCoordinate> m_gridItemCoordinate;
     OrderIterator m_orderIterator;
 };
 
 inline RenderGrid* toRenderGrid(RenderObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderGrid());
     return static_cast<RenderGrid*>(object);
 }
 
 inline const RenderGrid* toRenderGrid(const RenderObject* object)
 {
     ASSERT_WITH_SECURITY_IMPLICATION(!object || object->isRenderGrid());
     return static_cast<const RenderGrid*>(object);
 }
 
 // Catch unneeded cast.
 void toRenderGrid(const RenderGrid*);
 
 } // namespace WebCore
 
 #endif // RenderGrid_h