NamedLineCollection::NamedLineCollection in GridPositionsResolver.cpp does things like

    const NamedGridLinesMap& gridLineNames = isRowAxis ? gridContainerStyle.namedGridColumnLines() : gridContainerStyle.namedGridRowLines();
    auto linesIterator = gridLineNames.find(namedLine);
    m_namedLinesIndexes = linesIterator == gridLineNames.end() ? nullptr : &linesIterator->value;

where NamedGridLinesMap is a HashMap<String, Vector<unsigned>>

According to Darin Adler from bug 209572 comment #2,
> It’s really risky to store a pointer to a value slot in a HashMap. If any
> change is made to the map, adding or removing anything, rehashing means the
> pointer can end up invalid. Worse, it’s basically unpredictable how often
> this will happen so you could do a lot of testing and never observe it.

So a different approach should be used.