Optimize collapsed border painting

third_party/WebKit/Source/core/style/CollapsedBorderValue.h

 /*
  * Copyright (C) 2000 Lars Knoll (knoll@kde.org)
  *           (C) 2000 Antti Koivisto (koivisto@kde.org)
  *           (C) 2000 Dirk Mueller (mueller@kde.org)
  * Copyright (C) 2003, 2005, 2006, 2007, 2008 Apple Inc. All rights reserved.
  * Copyright (C) 2006 Graham Dennis (graham.dennis@gmail.com)
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
@@ skipping 52 matching lines @@
     bool isSameIgnoringColor(const CollapsedBorderValue& o) const
     {
         return width() == o.width() && style() == o.style() && precedence() == o.precedence();
     }
 
     bool equals(const CollapsedBorderValue& o) const
     {
         return color() == o.color() && isTransparent() == o.isTransparent() && isSameIgnoringColor(o);
     }
 
+    bool isVisible() const
+    {
+        return style() > BHIDDEN && !isTransparent() && exists();
+    }
+
     bool shouldPaint(const CollapsedBorderValue& tableCurrentBorderValue) const
     {
-        return style() > BHIDDEN && !isTransparent() && exists() && isSameIgnoringColor(tableCurrentBorderValue);
+        return isVisible() && isSameIgnoringColor(tableCurrentBorderValue);

[Julien - ping for review, 2016/01/08 14:18:15]

Shouldn't this be ASSERT(isVisible()) as we don't want to see invisible borders
when painting?

Overall we should add more performance ASSERTs to make sure we don't have a bug
adding those back down the road.

[Xianzhu, 2016/01/08 17:50:45]

A cell may have e.g. 2 visible borders and 2 invisible borders. In the case we
need to check shouldPaint() during painting also for the invisible borders, so
we can't assert here.

[Julien - ping for review, 2016/01/11 18:11:36]

OK!

+    }
+
+    bool isEquivalentForPainting(const CollapsedBorderValue& o) const
+    {
+        if (!isVisible() && !o.isVisible())
+            return true;
+        return equals(o);
     }
 
 private:
     Color m_color;
     unsigned m_colorIsCurrentColor : 1;
     unsigned m_width : 23;
     unsigned m_style : 4; // EBorderStyle
     unsigned m_precedence : 3; // EBorderPrecedence
     unsigned m_transparent : 1;
 };
 
 } // namespace blink
 
 #endif // CollapsedBorderValue_h