Bug
1073336 part 11 - Move GetAnimationPlayers to base CommonAnimationManager class; r=dbaron
nsAnimationManager provides GetAnimationPlayers while nsTransitionManager
provides GetElementTransitions. Both perform the same function, namely, fetching
(and optionally creating if it does not exist) the AnimationPlayerCollection for
the specified element/pseudo. Furthermore, both take the same arguments.
This patch aligns the method names and makes this a virtual method on the base
class CommonAnimationManager so that it can be used generically from a pointer
to a CommonAnimationManager.