This is an imperfect workaround. Ideally we'd want layout to determine the
correct color here: If the pushed layer will end up on something mostly opaque
in the outer layer, the font smoothing background color should be transparent
(or even a color that approximates that opaque content), and if the pushed
layer will end up on transparency in the outer layer, the appropriate font
smoothing background color for the outer layer should be used when drawing text
in the pushed layer.
This workaround causes us to lose subpixel AA in background tabs that have the
overflow mask applied to them. For those, using the font smoothing background
color in the pushed layer was the right choice.
MozReview-Commit-ID: FPufh04EVp3
--HG--
extra : rebase_source : 7a6cb73255bdb7f1b8aba7df60ebe61171275da4
b7d6066c45