Rework image_cache_task to avoid using `url` as key during the loading of an image.
Rework image_cache_task to avoid using `url` as key during the loading of an image.

A `url` can be very large, in particular if it is a data: url, so using it as a key for lookups whenever we load a few bytes is not a very good idea. This patch introduces an intermediate `LoadKey` (internally, an u64) that makes hashmap lookups faster. Somewhere along the way, we also get rid of a few calls to `url.clone()`.

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