style: Pass a bonafide nsACString to Servo.
style: Pass a bonafide nsACString to Servo.

This will allow the Rust code hold a copy-free strong reference to the string
past callstack unwind.

Bug: 1454460
Reviewed-by: bz
MozReview-Commit-ID: HCop9h2abZU

avadacatavra/servo,splav/servo,ConnorGBrewster/servo,peterjoel/servo,notriddle/servo,splav/servo,ConnorGBrewster/servo,avadacatavra/servo,dati91/servo,larsbergstrom/servo,saneyuki/servo,peterjoel/servo,larsbergstrom/servo,larsbergstrom/servo,nnethercote/servo,ConnorGBrewster/servo,mbrubeck/servo,larsbergstrom/servo,paulrouget/servo,avadacatavra/servo,szeged/servo,KiChjang/servo,larsbergstrom/servo,paulrouget/servo,paulrouget/servo,mbrubeck/servo,notriddle/servo,canaltinova/servo,szeged/servo,szeged/servo,larsbergstrom/servo,szeged/servo,avadacatavra/servo,DominoTree/servo,canaltinova/servo,splav/servo,DominoTree/servo,KiChjang/servo,splav/servo,SimonSapin/servo,canaltinova/servo,saneyuki/servo,nnethercote/servo,emilio/servo,sadmansk/servo,jimberlage/servo,pyfisch/servo,DominoTree/servo,szeged/servo,peterjoel/servo,jimberlage/servo,KiChjang/servo,saneyuki/servo,notriddle/servo,cbrewster/servo,emilio/servo,saneyuki/servo,paulrouget/servo,splav/servo,nnethercote/servo,DominoTree/servo,peterjoel/servo,saneyuki/servo,saneyuki/servo,KiChjang/servo,mbrubeck/servo,szeged/servo,SimonSapin/servo,jimberlage/servo,paulrouget/servo,paulrouget/servo,emilio/servo,cbrewster/servo,jimberlage/servo,paulrouget/servo,sadmansk/servo,peterjoel/servo,canaltinova/servo,dati91/servo,canaltinova/servo,pyfisch/servo,nnethercote/servo,KiChjang/servo,SimonSapin/servo,nnethercote/servo,nnethercote/servo,avadacatavra/servo,KiChjang/servo,notriddle/servo,avadacatavra/servo,szeged/servo,pyfisch/servo,peterjoel/servo,larsbergstrom/servo,pyfisch/servo,notriddle/servo,saneyuki/servo,emilio/servo,splav/servo,dati91/servo,DominoTree/servo,emilio/servo,avadacatavra/servo,larsbergstrom/servo,larsbergstrom/servo,notriddle/servo,cbrewster/servo,notriddle/servo,dati91/servo,notriddle/servo,saneyuki/servo,saneyuki/servo,szeged/servo,pyfisch/servo,nnethercote/servo,dati91/servo,pyfisch/servo,KiChjang/servo,cbrewster/servo,sadmansk/servo,splav/servo,DominoTree/servo,canaltinova/servo,pyfisch/servo,dati91/servo,peterjoel/servo,sadmansk/servo,emilio/servo,splav/servo,mbrubeck/servo,jimberlage/servo,SimonSapin/servo,DominoTree/servo,cbrewster/servo,paulrouget/servo,sadmansk/servo,mbrubeck/servo,notriddle/servo,peterjoel/servo,pyfisch/servo,splav/servo,DominoTree/servo,ConnorGBrewster/servo,saneyuki/servo,paulrouget/servo,peterjoel/servo,cbrewster/servo,pyfisch/servo,sadmansk/servo,SimonSapin/servo,ConnorGBrewster/servo,mbrubeck/servo,cbrewster/servo,mbrubeck/servo,sadmansk/servo,szeged/servo,SimonSapin/servo,nnethercote/servo,mbrubeck/servo,SimonSapin/servo,ConnorGBrewster/servo,jimberlage/servo,DominoTree/servo,paulrouget/servo,jimberlage/servo,emilio/servo,emilio/servo,KiChjang/servo,pyfisch/servo,splav/servo,dati91/servo,jimberlage/servo,larsbergstrom/servo,nnethercote/servo,emilio/servo,canaltinova/servo,notriddle/servo,dati91/servo,DominoTree/servo,nnethercote/servo,avadacatavra/servo,ConnorGBrewster/servo,ConnorGBrewster/servo,KiChjang/servo,sadmansk/servo,canaltinova/servo,KiChjang/servo,peterjoel/servo,cbrewster/servo,SimonSapin/servo,szeged/servo,emilio/servo,jimberlage/servo