The QML compiler can run asynchronously and produce ranges that don't
match up with other QML/JS ranges. The flame graph model assumes that
all ranges are perfectly nested, and produces incorrect data if they
aren't. The compile ranges are perfectly nested among themselves, and
the other QML/JS ranges are also perfectly nested among themselves, so
we can fix this by keeping separate stacks for them.

Change-Id: If4ea251c6a2e74bd04e142cf184937600ea31a87
Reviewed-by: Kai Koehne <kai.koehne@qt.io>