Bug 1325878: Allow creating empty Servo MediaList. r=xidorn
Bug 1325878: Allow creating empty Servo MediaList. r=xidorn

MozReview-Commit-ID: H7owjPB8dRi
Signed-off-by: Emilio Cobos Álvarez <86fa523305b8ad6a8a853c04cfef24a0445908d3@crisal.io>

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