CSS animations stuck; we should remove the backout infrastructure.
I probably should have commented here, but I already have a patch for this.
Created attachment 540174 [details] [diff] [review] patch
Oh... I'd been working on this since setting the assignee, oh well it happens :-)
Hmmm. I had hoped this would look like a straight backout of https://hg.mozilla.org/mozilla-central/rev/5f6f0204b682 but it appears to leave a bunch of the ordering wrong. I suspect that many parts of that patch will still reverse-apply cleanly, though, so it should be straightforward to revert it (and perhaps even more straightforward to backout and hg merge, and then perhaps diff rather than committing the backout).
Created attachment 540182 [details] [diff] [review] patch Done.
Created attachment 540559 [details] [diff] [review] patch That isn't quite right either, since it isn't merged to the trunk. Here's the result of a backout and merge, adjusted for the new changes (nsICSSRule.h -> Rule.h and the added code in nsStyleSet.cpp). This is actually a lot more similar to the first patch than the second, since the second wasn't relative to current trunk.