Issue #3416141 by gorkagr, Jaypan, Wim Leers, alexpott: big_pipe.js'...

    // occur if the script node was first observed with empty content and then

    // the child text node was added in full later.

    // @see `@ingroup large_chunk` for more information.

    else if (checkMutation(node.parentNode)) {

    // If an element is added and then immediately (faster than the next

    // setImmediate is triggered) removed to a watched element of a

    // MutationObserver, the observer will notice and add a mutation for both

    // the addedNode and the removedNode - but the referenced element will not

    // have a parent node.

    else if (node.parentNode !== null && checkMutation(node.parentNode)) {

      processReplacement(node.parentNode);

    }

  }