return NS_ERROR_FAILURE;
return NS_ERROR_OUT_OF_MEMORY;
NS_IMETHODIMP nsAccessibleTreeWalker::PushState(){  // Duplicate mState and put right before end; reset mState; make mState the new end of the stack  WalkState* nextToLastState= new WalkState();  if (!nextToLastState)    return NS_ERROR_FAILURE;  *nextToLastState = mState;  // Deep copy - copy contents of struct to new state that will be added to end of our stack  ClearState();  mState.prevState = nextToLastState;   // Link to previous state  return NS_OK;}