This accounts for the fact that in some cases we may not apply all of the
requested paint metrics from the APZ, leaving the two sides of the
GeckoContentController interface out of sync (on purpose).
This aligns display ports to tile boundaries, taking care to compensate for
the difference between the requested scroll position and the actual scroll
position.
This aligns display ports to tile boundaries, taking care to compensate for
the difference between the requested scroll position and the actual scroll
position.