visibleIndexOfNid method
Visible-order index for the live nid nid, or
VisibleOrderBuffer.kNotVisible when nid is not currently in the
visible order. O(1) typed-data read; no TKey hash. Hot-path
equivalent of _order.indexByNid[nid].
Caller must guarantee nid is live and within range.
Implementation
int visibleIndexOfNid(int nid) {
_ensureVisibleOrder();
return _order.indexByNid[nid];
}