Have HTMLCollection::item() return an Element as per specification

Source/core/html/HTMLTableRowElement.cpp

Index: Source/core/html/HTMLTableRowElement.cpp
diff --git a/Source/core/html/HTMLTableRowElement.cpp b/Source/core/html/HTMLTableRowElement.cpp
index 7e33eb433e7cbb7f227e5d173b68eb340f45a2a4..c54defc902ea0f18e7e6af14a0c167f43026f63f 100644
--- a/Source/core/html/HTMLTableRowElement.cpp
+++ b/Source/core/html/HTMLTableRowElement.cpp
@@ -142,7 +142,7 @@ void HTMLTableRowElement::deleteCell(int index, ExceptionState& exceptionState)
     if (index == -1)
         index = numCells-1;
     if (index >= 0 && index < numCells) {
-        RefPtr<Node> cell = children->item(index);
+        RefPtr<Element> cell = children->item(index);
         HTMLElement::removeChild(cell.get(), exceptionState);
     } else {
         exceptionState.throwDOMException(IndexSizeError, "The value provided (" + String::number(index) + ") is outside the range [0, " + String::number(numCells) + ").");