Simplify LayoutDocument::root_node.
Simplify LayoutDocument::root_node.

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