auto merge of #4186 : mbrubeck/servo/layout-viewer, r=glennw
auto merge of #4186 : mbrubeck/servo/layout-viewer, r=glennw

d1b433a3b3bab353f320b2f39fa953ce326d2d55 changed the encoding format for Flows.  The root is no longer wrapped inside a `data` field, but instead includes BaseFlow fields directly.  This broke the layout trace viewer, which threw an uncaught exception when the `data` property was missing.  This fixes the exception, though some functionality may still be partly broken.

eddyb/servo,steveklabnik/servo,jlegendary/servo,dati91/servo,walac/servo,nerith/servo,wpgallih/servo,GyrosOfWar/servo,canaltinova/servo,avadacatavra/servo,deokjinkim/servo,evilpie/servo,rixrix/servo,KiChjang/servo,notriddle/servo,sadmansk/servo,upsuper/servo,luniv/servo,saneyuki/servo,ConnorGBrewster/servo,nnethercote/servo,jlegendary/servo,wpgallih/servo,hyowon/servo,echochamber/servo,saratang/servo,pyfisch/servo,RenaudParis/servo,mt2d2/servo,vks/servo,g-k/servo,GreenRecycleBin/servo,dmarcos/servo,rixrix/servo,avadacatavra/servo,anthgur/servo,dati91/servo,wartman4404/servo,steveklabnik/servo,jimberlage/servo,emilio/servo,szeged/servo,RenaudParis/servo,codemac/servo,aidanhs/servo,jgraham/servo,indykish/servo,szeged/servo,paulrouget/servo,wpgallih/servo,notriddle/servo,avadacatavra/servo,tempbottle/servo,codemac/servo,nnethercote/servo,Adenilson/prototype-viewing-distance,froydnj/servo,boghison/servo,rentongzhang/servo,deokjinkim/servo,notriddle/servo,paulrouget/servo,nnethercote/servo,thiagopnts/servo,caldwell/servo,mdibaiee/servo,ruud-v-a/servo,saratang/servo,peterjoel/servo,chotchki/servo,mbrubeck/servo,peterjoel/servo,tafia/servo,wartman4404/servo,dsandeephegde/servo,chotchki/servo,peterjoel/servo,DominoTree/servo,A-deLuna/servo,hyowon/servo,GyrosOfWar/servo,emilio/servo,youprofit/servo,s142857/servo,j3parker/servo,cbrewster/servo,kindersung/servo,deokjinkim/servo,s142857/servo,ruud-v-a/servo,akosel/servo,nick-thompson/servo,nick-thompson/servo,jlegendary/servo,tschneidereit/servo,mt2d2/servo,RenaudParis/servo,splav/servo,karlito40/servo,RenaudParis/servo,wpgallih/servo,wartman4404/servo,chotchki/servo,jimberlage/servo,dvberkel/servo,nrc/servo,dvberkel/servo,fiji-flo/servo,jimberlage/servo,jimberlage/servo,dsandeephegde/servo,s142857/servo,g-k/servo,michaelwu/servo,nrc/servo,deokjinkim/servo,pyfisch/servo,zentner-kyle/servo,samfoo/servo,GreenRecycleBin/servo,DominoTree/servo,RenaudParis/servo,sadmansk/servo,larsbergstrom/servo,youprofit/servo,mt2d2/servo,runarberg/servo,meh/servo,A-deLuna/servo,ConnorGBrewster/servo,emilio/servo,youprofit/servo,jimberlage/servo,DominoTree/servo,meh/servo,GreenRecycleBin/servo,mdibaiee/servo,nick-thompson/servo,jimberlage/servo,KiChjang/servo,evilpie/servo,luniv/servo,wpgallih/servo,huonw/servo,kindersung/servo,mt2d2/servo,rentongzhang/servo,dati91/servo,dvberkel/servo,zhangjunlei26/servo,RenaudParis/servo,KiChjang/servo,nerith/servo,splav/servo,rixrix/servo,boghison/servo,szeged/servo,karlito40/servo,pgonda/servo,akosel/servo,anthgur/servo,DominoTree/servo,saratang/servo,larsbergstrom/servo,brendandahl/servo,SimonSapin/servo,notriddle/servo,bjwbell/servo,bjwbell/servo,splav/servo,dati91/servo,tempbottle/servo,huonw/servo,luniv/servo,saneyuki/servo,vks/servo,runarberg/servo,CJ8664/servo,jdramani/servo,mattnenterprise/servo,thiagopnts/servo,tempbottle/servo,nnethercote/servo,SimonSapin/servo,caldwell/servo,A-deLuna/servo,rentongzhang/servo,karlito40/servo,wpgallih/servo,aweinstock314/servo,larsbergstrom/servo,wartman4404/servo,GreenRecycleBin/servo,rentongzhang/servo,avadacatavra/servo,youprofit/servo,fiji-flo/servo,samfoo/servo,sadmansk/servo,mt2d2/servo,huonw/servo,indykish/servo,echochamber/servo,emilio/servo,dmarcos/servo,KiChjang/servo,snf/servo,AnthonyBroadCrawford/servo,dsandeephegde/servo,tafia/servo,youprofit/servo,upsuper/servo,g-k/servo,aweinstock314/servo,upsuper/servo,mbrubeck/servo,fiji-flo/servo,AnthonyBroadCrawford/servo,szeged/servo,canaltinova/servo,hyowon/servo,deokjinkim/servo,notriddle/servo,dmarcos/servo,fiji-flo/servo,zhangjunlei26/servo,j3parker/servo,nerith/servo,SimonSapin/servo,nnethercote/servo,ruud-v-a/servo,paulrouget/servo,zhangjunlei26/servo,mt2d2/servo,karlito40/servo,AnthonyBroadCrawford/servo,akosel/servo,notriddle/servo,j3parker/servo,rnestler/servo,rnestler/servo,nick-thompson/servo,boghison/servo,meh/servo,s142857/servo,kindersung/servo,indykish/servo,DominoTree/servo,larsbergstrom/servo,zentner-kyle/servo,pgonda/servo,jgraham/servo,youprofit/servo,eddyb/servo,KiChjang/servo,cbrewster/servo,SimonSapin/servo,nerith/servo,paulrouget/servo,WriterOfAlicrow/servo,samfoo/servo,dati91/servo,A-deLuna/servo,CJ8664/servo,caldwell/servo,tschneidereit/servo,j3parker/servo,snf/servo,larsbergstrom/servo,s142857/servo,GreenRecycleBin/servo,fiji-flo/servo,larsbergstrom/servo,echochamber/servo,zhangjunlei26/servo,rentongzhang/servo,ryancanhelpyou/servo,KiChjang/servo,michaelwu/servo,thiagopnts/servo,pyfisch/servo,saneyuki/servo,rixrix/servo,zhangjunlei26/servo,deokjinkim/servo,evilpie/servo,vks/servo,saneyuki/servo,nick-thompson/servo,notriddle/servo,WriterOfAlicrow/servo,rnestler/servo,splav/servo,dsandeephegde/servo,aidanhs/servo,saratang/servo,dvberkel/servo,DominoTree/servo,avadacatavra/servo,paulrouget/servo,ryancanhelpyou/servo,vks/servo,j3parker/servo,CJ8664/servo,codemac/servo,aweinstock314/servo,saratang/servo,youprofit/servo,wartman4404/servo,samfoo/servo,jimberlage/servo,anthgur/servo,zentner-kyle/servo,srbhklkrn/SERVOENGINE,bjwbell/servo,rn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son/prototype-viewing-distance,vks/servo,upsuper/servo,tempbottle/servo,caldwell/servo,peterjoel/servo,fiji-flo/servo,szeged/servo,larsbergstrom/servo,saneyuki/servo,tschneidereit/servo,chotchki/servo,jdramani/servo,echochamber/servo,brendandahl/servo,froydnj/servo,ryancanhelpyou/servo,luniv/servo,snf/servo,jimberlage/servo,jimberlage/servo,saneyuki/servo,jdramani/servo,dati91/servo,upsuper/servo,upsuper/servo,rnestler/servo,aweinstock314/servo,cbrewster/servo,thiagopnts/servo,boghison/servo,brendandahl/servo,pgonda/servo,dhananjay92/servo,srbhklkrn/SERVOENGINE,zhangjunlei26/servo,luniv/servo,saneyuki/servo,szeged/servo,GyrosOfWar/servo,A-deLuna/servo,cbrewster/servo,samfoo/servo,dmarcos/servo,DominoTree/servo,ruud-v-a/servo,nnethercote/servo,DominoTree/servo,Adenilson/prototype-viewing-distance,codemac/servo,cbrewster/servo,mattnenterprise/servo,caldwell/servo,peterjoel/servo,rnestler/servo,huonw/servo,aweinstock314/servo,canaltinova/servo,splav/servo,rixrix/servo,AnthonyBroadCrawford/servo,GyrosOfWar/servo,pyecs/servo,pgonda/servo,tempbottle/servo,avadacatavra/servo,walac/servo,wartman4404/servo,mbrubeck/servo,sadmansk/servo,tschneidereit/servo,rentongzhang/servo,KiChjang/servo,snf/servo,boghison/servo,walac/servo,canaltinova/servo,srbhklkrn/SERVOENGINE,AnthonyBroadCrawford/servo,boghison/servo,luniv/servo,anthgur/servo,snf/servo,zhangjunlei26/servo,WriterOfAlicrow/servo,froydnj/servo,ConnorGBrewster/servo,mattnenterprise/servo,mdibaiee/servo,pgonda/servo,zentner-kyle/servo,dagnir/servo,dhananjay92/servo,hyowon/servo,chotchki/servo,avadacatavra/servo,eddyb/servo