Use tighter typing in table rendering code

Source/core/rendering/RenderTableCell.cpp

Index: Source/core/rendering/RenderTableCell.cpp
diff --git a/Source/core/rendering/RenderTableCell.cpp b/Source/core/rendering/RenderTableCell.cpp
index fec275c19214ff55cfb6337751ef0000fd77f4a0..179901397f0d77dcb5a5921d7ed3224ed261576e 100644
--- a/Source/core/rendering/RenderTableCell.cpp
+++ b/Source/core/rendering/RenderTableCell.cpp
@@ -741,7 +741,7 @@ CollapsedBorderValue RenderTableCell::computeCollapsedBeforeBorder(IncludeBorder
         if (prevCell->section() == section())
             prevRow = parent()->previousSibling();
         else
-            prevRow = prevCell->section()->lastChild();
+            prevRow = prevCell->section()->lastRow();
 
         if (prevRow) {
             result = chooseBorder(CollapsedBorderValue(prevRow->style()->borderAfter(), includeColor ? prevRow->resolveColor(afterColorProperty) : Color(), BROW), result);