PL_ARENA_ALLOCATE(NS_REINTERPRET_CAST(void*,aNode), &aPool, sizeof(DisplayZTreeNode));
ARENA_ALLOCATE(aNode, &aPool, DisplayZTreeNode);
static nsresult EnsureZTreeNodeCreated(nsView* aView, DisplayZTreeNode* &aNode, PLArenaPool &aPool){  if (nsnull == aNode) {    PL_ARENA_ALLOCATE(NS_REINTERPRET_CAST(void*,aNode), &aPool, sizeof(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;}