compute_dependencies() is only used internally by GtkCssStaticStyle, so there's no need to have it elsewhere.
GtkCssStyle is the base class to be used for all types of styles that do exist. GtkCssAnimatedStyle is the only implementation so far, that is exactly a copy/paste of the old GtkCssStyle code.
This is literally just renaming of the object (and the associated source files). No other changes are in there.