Created attachment 472698 [details] [diff] [review]
do the clear
This caused stuff to "build up", that is to have things like antialiased areas to get bolder and bolder. We need to clear this out, just like we do in the d3d9 backend.
This could probably use a test, but I'm not sure how to construct one -- way to reproduce is to have a colored div with opacity: 0.2 with opacity changing to 0.4 on hover. Moving the mouse over it and off it should swap between the two opacities, though without this patch it just gets darker and darker.
This fixes a large number of visual artifacts with gl layers.
This was committed a while back. http://hg.mozilla.org/mozilla-central/rev/c1346180e12a