Move parallel_traversal from LayoutTaskData to LayoutTask.
Move parallel_traversal from LayoutTaskData to LayoutTask.

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