Optimize collapsed border painting

third_party/WebKit/Source/core/layout/LayoutTableCell.h

Index: third_party/WebKit/Source/core/layout/LayoutTableCell.h
diff --git a/third_party/WebKit/Source/core/layout/LayoutTableCell.h b/third_party/WebKit/Source/core/layout/LayoutTableCell.h
index 643d7e3289f8fd64bb8c974f241f479a1c2e4f34..da49efd6fe78cc9c3bf52b6b162eec3af2c8ceda 100644
--- a/third_party/WebKit/Source/core/layout/LayoutTableCell.h
+++ b/third_party/WebKit/Source/core/layout/LayoutTableCell.h
@@ -272,6 +272,14 @@ public:
 
     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;
@@ -357,6 +365,8 @@ private:
     // 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());