By passing the startTime as a TimeDuration we are able to represent times in the
distant past (and with the same range as we can represent on the main thread so
that if we do encounter range errors in future, they should not differ between
the main thread and the compositor).
This patch includes a crashtest. I have verified that, without the code changes
included in this patch, this crashtest fails on debug builds on OSX.
MozReview-Commit-ID: EDuKLzfEC0K
--HG--
extra : rebase_source : 1883080fdfac8c33f70698145f21e67cbdfdd4f2
5267613207