Bug 1352067 - Initialize StyleAnimationValue with zeros.
Bug 1352067 - Initialize StyleAnimationValue with zeros.

AnimationValue::mGecko and AnimationValue::mServo are mutually
exclusive, so we have to make sure mGecko.IsNull() returns reasonable
value, or we will got assertions. Hence, we should initialize it during
constructing StyleAnimationValue from Servo side.

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