HTMLTableSectionElement.insertRow(0) / HTMLTableRowElement.insertCell(0) do not behave correctly

Source/core/html/HTMLTableRowElement.cpp

 /*
  * Copyright (C) 1997 Martin Jones (mjones@kde.org)
  *           (C) 1997 Torben Weis (weis@kde.org)
  *           (C) 1998 Waldo Bastian (bastian@kde.org)
  *           (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 1999 Antti Koivisto (koivisto@kde.org)
  * Copyright (C) 2003, 2004, 2005, 2006, 2007, 2010 Apple Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
@@ skipping 117 matching lines @@
 PassRefPtr<HTMLElement> HTMLTableRowElement::insertCell(int index, ExceptionState& exceptionState)
 {
     RefPtr<HTMLCollection> children = cells();
     int numCells = children ? children->length() : 0;
     if (index < -1 || index > numCells) {
         exceptionState.throwDOMException(IndexSizeError, "The value provided (" + String::number(index) + ") is outside the range [-1, " + String::number(numCells) + "].");
         return nullptr;
     }
 
     RefPtr<HTMLTableCellElement> cell = HTMLTableCellElement::create(tdTag, document());
-    if (index < 0 || index >= numCells)
+    if (numCells == index || index == -1)
         appendChild(cell, exceptionState);
-    else {
-        Node* n;
-        if (index < 1)
-            n = firstChild();
-        else
-            n = children->item(index);
-        insertBefore(cell, n, exceptionState);
-    }
+    else
+        insertBefore(cell, children->item(index), exceptionState);
     return cell.release();
 }
 
 void HTMLTableRowElement::deleteCell(int index, ExceptionState& exceptionState)
 {
     RefPtr<HTMLCollection> children = cells();
     int numCells = children ? children->length() : 0;
     if (index == -1)
         index = numCells-1;
     if (index >= 0 && index < numCells) {
         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) + ").");
     }
 }
 
 PassRefPtr<HTMLCollection> HTMLTableRowElement::cells()
 {
     return ensureCachedHTMLCollection(TRCells);
 }
 
 }