Auto merge of #9210 - ecoal95:webgl-task-in-thread, r=jdm
Auto merge of #9210 - ecoal95:webgl-task-in-thread, r=jdm

webgl: Create the paint task object in the thread

This avoids problems like:
https://github.com/servo/servo/issues/9006#issuecomment-170007845

See that conversation for more details.

<!-- Reviewable:start -->
[<img src="https://reviewable.io/review_button.png" height=40 alt="Review on Reviewable"/>](https://reviewable.io/reviews/servo/servo/9210)
<!-- Reviewable:end -->

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