For doing this, ServoComputedData is split into separate files, so that
files don't need to include ServoBindings.h just for accessing style
structs from ComputedStyles.
MozReview-Commit-ID: DPAd7PUUCl9
--HG--
extra : rebase_source : 7d6f739b7fb58a46e1624ba62e717412057ea9c1