Optimize collapsed border painting

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

Index: third_party/WebKit/Source/core/style/CollapsedBorderValue.h
diff --git a/third_party/WebKit/Source/core/style/CollapsedBorderValue.h b/third_party/WebKit/Source/core/style/CollapsedBorderValue.h
index b184ce2aded2c1080de34b85e0e9f661c794b8e4..e28fc6cb8532c06ed35310ada569039ed28e2f89 100644
--- a/third_party/WebKit/Source/core/style/CollapsedBorderValue.h
+++ b/third_party/WebKit/Source/core/style/CollapsedBorderValue.h
@@ -65,8 +65,10 @@ public:
         return width() == o.width() && style() == o.style() && precedence() == o.precedence();
     }
 
-    bool equals(const CollapsedBorderValue& o) const
+    bool visuallyEquals(const CollapsedBorderValue& o) const
     {
+        if (!isVisible() && !o.isVisible())
+            return true;

[Xianzhu, 2016/05/03 19:03:27]

Previously cell borders were cached in LayoutTableSection, separately for the 4
sides and invisible borders were not cached. If a new border previously
invisible is now still invisible (though with some of other fields changed), we
not cache it, and treat it as not changed.

Now we need the above change to treat invisible borders which is previously
invisible unchanged no matter of other fields. This is because now we cache the
4 borders (including invisible ones) of a cell in the same structure, when any
of the borders is visible.

         return color() == o.color() && isTransparent() == o.isTransparent() && isSameIgnoringColor(o);
     }
 
@@ -77,9 +79,7 @@ public:
 
     bool shouldPaint(const CollapsedBorderValue& tableCurrentBorderValue) const
     {
-        // Invisible borders are not cached so painters see visible borders only.
-        ASSERT(isVisible());
-        return isSameIgnoringColor(tableCurrentBorderValue);
+        return isVisible() && isSameIgnoringColor(tableCurrentBorderValue);

[Xianzhu, 2016/05/03 19:03:27]

The reason of this change is the same as the above one.

     }
 
 private: