Let collapsed border drawings be cacheable

Source/core/layout/LayoutTableSection.h

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2009, 2013 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 192 matching lines @@
     }
 
     bool needsCellRecalc() const { return m_needsCellRecalc; }
     void setNeedsCellRecalc();
 
     LayoutUnit rowBaseline(unsigned row) { return m_grid[row].baseline; }
 
     void rowLogicalHeightChanged(LayoutTableRow*);
 
     void removeCachedCollapsedBorders(const LayoutTableCell*);
-    void setCachedCollapsedBorder(const LayoutTableCell*, CollapsedBorderSide, const CollapsedBorderValue&);
+    bool setCachedCollapsedBorder(const LayoutTableCell*, CollapsedBorderSide, const CollapsedBorderValue&);

[pdr., 2015/08/20 07:07:15]

Please add a comment explaining the return value.

// Return true if the collapsed borders change.

[Xianzhu, 2015/08/20 16:39:51]

Done.

     const CollapsedBorderValue& cachedCollapsedBorder(const LayoutTableCell*, CollapsedBorderSide) const;
 
     // distributeExtraLogicalHeightToRows methods return the *consumed* extra logical height.
     // FIXME: We may want to introduce a structure holding the in-flux layout information.
     int distributeExtraLogicalHeightToRows(int extraLogicalHeight);
 
     static LayoutTableSection* createAnonymousWithParent(const LayoutObject*);
     LayoutBox* createAnonymousBoxWithSameTypeAs(const LayoutObject* parent) const override
     {
         return createAnonymousWithParent(parent);
@@ skipping 90 matching lines @@
     // It is held at LayoutTableSection level to spare memory consumption by table cells.
     using CellsCollapsedBordersMap = HashMap<pair<const LayoutTableCell*, int>, CollapsedBorderValue>;
     CellsCollapsedBordersMap m_cellsCollapsedBorders;
 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutTableSection, isTableSection());
 
 } // namespace blink
 
 #endif // LayoutTableSection_h