HashCache: Apply trait bounds on type itself, rather than only the impl
HashCache: Apply trait bounds on type itself, rather than only the impl

I don't think there is any reason to keep the container more generic
than its (only) implementation -- the constraints are necessary for this
container to work at all.

Defining the constraints on the type itself also enables use
of #[derive(Debug)].

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