cleanUpParentStack = function(original, clone) {
    if (original === null) {
      return;
    }

    var cloneFull = original.getChildCount() == clone.getChildCount();
    if (cloneFull) {
      var cloneIndex = copyParentStack.indexOf(clone);
      if (cloneIndex != -1) {
        copyParentStack.splice(cloneIndex, 1);
      }
    }
  }
Removes a node from the parent stack, if that node has already reached its
target number of children.
@param {?lf.structs.TreeNode} original The original node.
@param {!lf.structs.TreeNode} clone The corresponding cloned node.