add 'slow' prefix to RenderObject's firstChild() / lastChild() methods

Source/core/rendering/FixedTableLayout.cpp

Index: Source/core/rendering/FixedTableLayout.cpp
diff --git a/Source/core/rendering/FixedTableLayout.cpp b/Source/core/rendering/FixedTableLayout.cpp
index 195d9af16cf68cc97a4c8ae7086f24b3aea3c61d..4d1eab50b6bfcbd837bb1be20b1321117862d4c3 100644
--- a/Source/core/rendering/FixedTableLayout.cpp
+++ b/Source/core/rendering/FixedTableLayout.cpp
@@ -137,7 +137,7 @@ int FixedTableLayout::calcWidthArray()
 
     unsigned currentColumn = 0;
 
-    RenderObject* firstRow = section->firstChild();
+    RenderTableRow* firstRow = toRenderTableRow(section->firstChild());
     for (RenderObject* child = firstRow->firstChild(); child; child = child->nextSibling()) {
         if (!child->isTableCell())
             continue;