Bug 260136

I expect the changes made in 266196@main for bug 240061 are not dealing with accelerated animations. Indeed, CoreAnimation doesn’t have any native equivalent to linear() so we’ll have to either find something that matches and add code to translate to the CA-native primitive or expand KeyframeEffect::canBeAccelerated() to do something similar to what we do with steps(). I argue for the latter because with the work for threaded animation resolution support for linear() will be free and I think it’s not a good idea to add more CA-specific code.