Use new is*Element() helper functions more in 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 e33032a80302afe9369836f8112134d7c8d2ce0a..b465f0eabe0b86fdde164ed68f239936633b6b87 100644
--- a/Source/core/rendering/RenderTableCell.cpp
+++ b/Source/core/rendering/RenderTableCell.cpp
@@ -75,16 +75,16 @@ void RenderTableCell::willBeRemovedFromTree()
 unsigned RenderTableCell::parseColSpanFromDOM() const
 {
     ASSERT(node());
-    if (node()->hasTagName(tdTag) || node()->hasTagName(thTag))
-        return min<unsigned>(toHTMLTableCellElement(node())->colSpan(), maxColumnIndex);
+    if (isHTMLTableCellElement(*node()))
+        return min<unsigned>(toHTMLTableCellElement(*node()).colSpan(), maxColumnIndex);
     return 1;
 }
 
 unsigned RenderTableCell::parseRowSpanFromDOM() const
 {
     ASSERT(node());
-    if (node()->hasTagName(tdTag) || node()->hasTagName(thTag))
-        return min<unsigned>(toHTMLTableCellElement(node())->rowSpan(), maxRowIndex);
+    if (isHTMLTableCellElement(*node()))
+        return min<unsigned>(toHTMLTableCellElement(*node()).rowSpan(), maxRowIndex);
     return 1;
 }
 
@@ -99,7 +99,7 @@ void RenderTableCell::updateColAndRowSpanFlags()
 void RenderTableCell::colSpanOrRowSpanChanged()
 {
     ASSERT(node());
-    ASSERT(node()->hasTagName(tdTag) || node()->hasTagName(thTag));
+    ASSERT(isHTMLTableCellElement(*node()));
 
     updateColAndRowSpanFlags();