Stylo doesn't have a good equivalent for restyle hints to expose in markers and
the ones exposed for Gecko aren't very accurate either, so we don't want to
expose the restyle hint anymore.
At the same time, several animation restyle tests currently use the hint inside
the marker to check when animation-only restyles have happened. We can preserve
this by changing the data inside the marker to be a flag for whether the restyle
is animation only, which we know for both Gecko and Stylo.
MozReview-Commit-ID: 8L8KU8Ush7P
b4554d4442