static nsresult EnsureZTreeNodeCreated(nsIView* aView, DisplayZTreeNode* &aNode) {
static nsresult EnsureZTreeNodeCreated(nsView* aView, DisplayZTreeNode* &aNode) {
static nsresult EnsureZTreeNodeCreated(nsIView* aView, DisplayZTreeNode* &aNode) {  if (nsnull == aNode) {    aNode = new DisplayZTreeNode;    if (nsnull == aNode) {      return NS_ERROR_OUT_OF_MEMORY;    }    aNode->mView = aView;    aNode->mDisplayElement = nsnull;    aNode->mZChild = nsnull;    aNode->mZSibling = nsnull;  }  return NS_OK;}