Optimize collapsed border painting

third_party/WebKit/Source/core/layout/LayoutTableCell.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, 2007, 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 254 matching lines @@
     bool isFirstOrLastCellInRow() const
     {
         return !table()->cellAfter(this) || !table()->cellBefore(this);
     }
 #endif
 
     const char* name() const override { return "LayoutTableCell"; }
 
     bool backgroundIsKnownToBeOpaqueInRect(const LayoutRect&) const override;
 
+    struct CollapsedBorderValues {
+        CollapsedBorderValue startBorder;
+        CollapsedBorderValue endBorder;
+        CollapsedBorderValue beforeBorder;
+        CollapsedBorderValue afterBorder;
+    };
+    const CollapsedBorderValues* collapsedBorderValues() const { return m_collapsedBorderValues.get(); }
+
 protected:
     void styleDidChange(StyleDifference, const ComputedStyle* oldStyle) override;
     void computePreferredLogicalWidths() override;
 
     void addLayerHitTestRects(LayerHitTestRects&, const PaintLayer* currentCompositedLayer, const LayoutPoint& layerOffset, const LayoutRect& containerRect) const override;
 
 private:
     bool isOfType(LayoutObjectType type) const override { return type == LayoutObjectTableCell || LayoutBlockFlow::isOfType(type); }
 
     void willBeRemovedFromTree() override;
@@ skipping 65 matching lines @@
     unsigned m_hasColSpan: 1;
     unsigned m_hasRowSpan: 1;
 
     // The intrinsic padding.
     // See class comment for what they are.
     //
     // Note: Those fields are using non-subpixel units (int)
     // because we don't do fractional arithmetic on tables.
     int m_intrinsicPaddingBefore;
     int m_intrinsicPaddingAfter;
+
+    OwnPtr<CollapsedBorderValues> m_collapsedBorderValues;

[chrishtr, 2016/05/04 23:24:18]

Is border collapsing common enough that we should just store it directly without
a pointer?

[Xianzhu, 2016/05/05 00:15:51]

It's not common: 6.9% cells have visible collapsed borders at least on one side.

 };
 
 DEFINE_LAYOUT_OBJECT_TYPE_CASTS(LayoutTableCell, isTableCell());
 
 inline LayoutTableCell* LayoutTableCell::previousCell() const
 {
     return toLayoutTableCell(LayoutObject::previousSibling());
 }
 
 inline LayoutTableCell* LayoutTableCell::nextCell() const
 {
     return toLayoutTableCell(LayoutObject::nextSibling());
 }
 
 inline LayoutTableCell* LayoutTableRow::firstCell() const
 {
     ASSERT(children() == virtualChildren());
     return toLayoutTableCell(children()->firstChild());
 }
 
 inline LayoutTableCell* LayoutTableRow::lastCell() const
 {
     ASSERT(children() == virtualChildren());
     return toLayoutTableCell(children()->lastChild());
 }
 
 } // namespace blink
 
 #endif // LayoutTableCell_h