Is your feature request related to a problem? Please describe.

Currently any changes to headers in CefRequest can result in header order changes, we can result in bot detection kicking in for some websites.

Any change to headers that sets Changed(kChangedHeaderMap); results in the headers being set from a std::multimap which may have a different ordering to the original net::HttpRequestHeaders

Describe the solution you'd like
Support modifying headers without effecting order.

Describe alternatives you've considered
Not aware of alternatives.

Additional context
Add any other context or screenshots about the feature request here.