Make derive_ methods accept a style struct rather than a computed_value, and do mutations internally.
Make derive_ methods accept a style struct rather than a computed_value, and do mutations internally.

This will allow us to specialize these methods for the gecko case without requiring the gecko path
to generate servo computed_values to pass to them.

DominoTree/servo,KiChjang/servo,nnethercote/servo,emilio/servo,avadacatavra/servo,rnestler/servo,pyfisch/servo,dsandeephegde/servo,cbrewster/servo,KiChjang/servo,anthgur/servo,upsuper/servo,sadmansk/servo,notriddle/servo,steveklabnik/servo,mattnenterprise/servo,KiChjang/servo,dati91/servo,emilio/servo,dsandeephegde/servo,upsuper/servo,fiji-flo/servo,anthgur/servo,KiChjang/servo,dsandeephegde/servo,dsandeephegde/servo,mbrubeck/servo,nnethercote/servo,dati91/servo,dati91/servo,dati91/servo,jimberlage/servo,jimberlage/servo,ConnorGBrewster/servo,rnestler/servo,saneyuki/servo,dsandeephegde/servo,paulrouget/servo,CJ8664/servo,dati91/servo,splav/servo,jimberlage/servo,cbrewster/servo,peterjoel/servo,paulrouget/servo,dsandeephegde/servo,paulrouget/servo,larsbergstrom/servo,szeged/servo,rnestler/servo,szeged/servo,ConnorGBrewster/servo,fiji-flo/servo,pyfisch/servo,DominoTree/servo,mbrubeck/servo,nnethercote/servo,dati91/servo,steveklabnik/servo,saneyuki/servo,cbrewster/servo,eddyb/servo,jimberlage/servo,SimonSapin/servo,ConnorGBrewster/servo,sadmansk/servo,notriddle/servo,CJ8664/servo,anthgur/servo,fiji-flo/servo,sadmansk/servo,emilio/servo,canaltinova/servo,emilio/servo,nrc/servo,jimberlage/servo,splav/servo,cbrewster/servo,nnethercote/servo,cbrewster/servo,notriddle/servo,nnethercote/servo,emilio/servo,larsbergstrom/servo,anthgur/servo,anthgur/servo,CJ8664/servo,splav/servo,emilio/servo,upsuper/servo,nnethercote/servo,paulrouget/servo,upsuper/servo,splav/servo,eddyb/servo,notriddle/servo,mattnenterprise/servo,sadmansk/servo,peterjoel/servo,mattnenterprise/servo,mbrubeck/servo,nrc/servo,szeged/servo,peterjoel/servo,mbrubeck/servo,thiagopnts/servo,DominoTree/servo,eddyb/servo,peterjoel/servo,avadacatavra/servo,pyfisch/servo,rnestler/servo,saneyuki/servo,szeged/servo,upsuper/servo,ConnorGBrewster/servo,nnethercote/servo,cbrewster/servo,notriddle/servo,DominoTree/servo,pyfisch/servo,canaltinova/servo,ConnorGBrewster/servo,nrc/servo,dati91/servo,ConnorGBrewster/servo,SimonSapin/servo,notriddle/servo,szeged/servo,mbrubeck/servo,saneyuki/servo,pyfisch/servo,mattnenterprise/servo,mattnenterprise/servo,nnethercote/servo,KiChjang/servo,nrc/servo,SimonSapin/servo,saneyuki/servo,steveklabnik/servo,thiagopnts/servo,peterjoel/servo,peterjoel/servo,pyfisch/servo,cbrewster/servo,mbrubeck/servo,canaltinova/servo,eddyb/servo,pyfisch/servo,canaltinova/servo,DominoTree/servo,CJ8664/servo,jimberlage/servo,ConnorGBrewster/servo,sadmansk/servo,eddyb/servo,thiagopnts/servo,thiagopnts/servo,larsbergstrom/servo,paulrouget/servo,paulrouget/servo,SimonSapin/servo,avadacatavra/servo,mattnenterprise/servo,canaltinova/servo,KiChjang/servo,rnestler/servo,larsbergstrom/servo,saneyuki/servo,peterjoel/servo,larsbergstrom/servo,notriddle/servo,steveklabnik/servo,canaltinova/servo,notriddle/servo,canaltinova/servo,CJ8664/servo,szeged/servo,KiChjang/servo,splav/servo,jimberlage/servo,nnethercote/servo,canaltinova/servo,larsbergstrom/servo,dsandeephegde/servo,DominoTree/servo,anthgur/servo,mattnenterprise/servo,CJ8664/servo,steveklabnik/servo,sadmansk/servo,emilio/servo,SimonSapin/servo,DominoTree/servo,upsuper/servo,KiChjang/servo,szeged/servo,pyfisch/servo,splav/servo,notriddle/servo,larsbergstrom/servo,SimonSapin/servo,larsbergstrom/servo,avadacatavra/servo,saneyuki/servo,sadmansk/servo,KiChjang/servo,fiji-flo/servo,nnethercote/servo,saneyuki/servo,avadacatavra/servo,splav/servo,jimberlage/servo,nrc/servo,emilio/servo,SimonSapin/servo,DominoTree/servo,anthgur/servo,avadacatavra/servo,rnestler/servo,saneyuki/servo,dati91/servo,rnestler/servo,thiagopnts/servo,KiChjang/servo,mbrubeck/servo,pyfisch/servo,paulrouget/servo,peterjoel/servo,pyfisch/servo,thiagopnts/servo,szeged/servo,anthgur/servo,emilio/servo,eddyb/servo,dsandeephegde/servo,splav/servo,splav/servo,upsuper/servo,steveklabnik/servo,thiagopnts/servo,fiji-flo/servo,SimonSapin/servo,eddyb/servo,mbrubeck/servo,larsbergstrom/servo,avadacatavra/servo,DominoTree/servo,ConnorGBrewster/servo,jimberlage/servo,avadacatavra/servo,fiji-flo/servo,sadmansk/servo,CJ8664/servo,fiji-flo/servo,steveklabnik/servo,saneyuki/servo,larsbergstrom/servo,peterjoel/servo,splav/servo,upsuper/servo,nrc/servo,rnestler/servo,paulrouget/servo,CJ8664/servo,notriddle/servo,cbrewster/servo,eddyb/servo,paulrouget/servo,DominoTree/servo,szeged/servo,mattnenterprise/servo,thiagopnts/servo,emilio/servo,peterjoel/servo,fiji-flo/servo,nrc/servo,paulrouget/servo,szeged/servo