Improve messaging when registrationComplete hasn't been called
Improve messaging when registrationComplete hasn't been called

Summary:
The previous message from CHECK_THROW was difficult to debug.
This improves the messaging to be more actionable.

Test Plan: runtests

Reviewed By: lins@fb.com

Subscribers: lins, anca, fugalh

FB internal diff: D1483915

leolujuyi/folly,tomhughes/folly,bobegir/folly,SeanRBurton/folly,guker/folly,Hincoin/folly,xzmagic/folly,project-zerus/folly,fw1121/folly,stonegithubs/folly,bowlofstew/folly,bsampath/folly,nickhen/folly,stonegithubs/folly,fw1121/folly,lifei/folly,bikong2/folly,clearlylin/folly,bowlofstew/folly,reddit/folly,gavioto/folly,bobegir/folly,reddit/folly,tempbottle/folly,cole14/folly,renyinew/folly,doctaweeks/folly,alexst07/folly,facebook/folly,guker/folly,bowlofstew/folly,shaobz/folly,tempbottle/folly,gavioto/folly,sakishum/folly,loverszhaokai/folly,KSreeHarsha/folly,arg0/folly,fw1121/folly,mqeizi/folly,cppfool/folly,gaoyingie/folly,sonnyhu/folly,tomhughes/folly,floxard/folly,fw1121/folly,loverszhaokai/folly,theiver9827/folly,zhiweicai/folly,colemancda/folly,xzmagic/folly,arg0/folly,renyinew/folly,gaoyingie/folly,wildinto/folly,floxard/folly,wildinto/folly,raphaelamorim/folly,KSreeHarsha/folly,gavioto/folly,gavioto/folly,theiver9827/folly,doctaweeks/folly,cole14/folly,brunomorishita/folly,arg0/folly,gaoyingie/folly,facebook/folly,guker/folly,CJstar/folly,leolujuyi/folly,romange/folly,bobegir/folly,CJstar/folly,Hincoin/folly,kernelim/folly,cole14/folly,upsoft/folly,tomhughes/folly,juniway/folly,chjp2046/folly,rklabs/folly,SammyK/folly,Orvid/folly,charsyam/folly,kernelim/folly,CJstar/folly,Hincoin/folly,cole14/folly,juniway/folly,alexst07/folly,loversInJapan/folly,PPC64/folly,SeanRBurton/folly,chjp2046/folly,constantine001/folly,cole14/folly,bikong2/folly,upsoft/folly,wildinto/folly,brunomorishita/folly,loverszhaokai/folly,doctaweeks/folly,bowlofstew/folly,brunomorishita/folly,bsampath/folly,facebook/folly,PPC64/folly,Hincoin/folly,hongliangzhao/folly,loverszhaokai/folly,sonnyhu/folly,juniway/folly,hongliangzhao/folly,gavioto/folly,bowlofstew/folly,sakishum/folly,charsyam/folly,project-zerus/folly,wildinto/folly,SammyK/folly,bikong2/folly,bsampath/folly,yangjin-unique/folly,clearlylin/folly,PoisonBOx/folly,shaobz/folly,renyinew/folly,nickhen/folly,Eagle-X/folly,Orvid/folly,renyinew/folly,leolujuyi/folly,raphaelamorim/folly,lifei/folly,ykarlsbrun/folly,kernelim/folly,constantine001/folly,Hincoin/folly,theiver9827/folly,clearlylin/folly,alexst07/folly,SammyK/folly,tempbottle/folly,bobegir/folly,yangjin-unique/folly,SammyK/folly,romange/folly,alexst07/folly,upsoft/folly,nickhen/folly,rklabs/folly,mqeizi/folly,zhiweicai/folly,clearlylin/folly,cppfool/folly,loverszhaokai/folly,arg0/folly,Eagle-X/folly,chjp2046/folly,PoisonBOx/folly,PPC64/folly,floxard/folly,kernelim/folly,gaoyingie/folly,Orvid/folly,cppfool/folly,PPC64/folly,yangjin-unique/folly,loversInJapan/folly,chjp2046/folly,stonegithubs/folly,colemancda/folly,PPC64/folly,KSreeHarsha/folly,zhiweicai/folly,sakishum/folly,kernelim/folly,ykarlsbrun/folly,Orvid/folly,project-zerus/folly,upsoft/folly,project-zerus/folly,tomhughes/folly,zhiweicai/folly,tempbottle/folly,doctaweeks/folly,clearlinux/folly,brunomorishita/folly,reddit/folly,Eagle-X/folly,lifei/folly,romange/folly,Eagle-X/folly,guker/folly,gaoyingie/folly,Eagle-X/folly,chjp2046/folly,colemancda/folly,arg0/folly,juniway/folly,constantine001/folly,shaobz/folly,renyinew/folly,shaobz/folly,colemancda/folly,bsampath/folly,raphaelamorim/folly,xzmagic/folly,SeanRBurton/folly,raphaelamorim/folly,wildinto/folly,charsyam/folly,fw1121/folly,lifei/folly,mqeizi/folly,reddit/folly,clearlinux/folly,clearlinux/folly,reddit/folly,guker/folly,cppfool/folly,brunomorishita/folly,hongliangzhao/folly,SeanRBurton/folly,yangjin-unique/folly,rklabs/folly,constantine001/folly,clearlylin/folly,upsoft/folly,doctaweeks/folly,PoisonBOx/folly,sakishum/folly,floxard/folly,bobegir/folly,sonnyhu/folly,stonegithubs/folly,stonegithubs/folly,SeanRBurton/folly,bikong2/folly,PoisonBOx/folly,CJstar/folly,facebook/folly,sakishum/folly,Orvid/folly,leolujuyi/folly,bsampath/folly,loversInJapan/folly,tempbottle/folly,yangjin-unique/folly,xzmagic/folly,cppfool/folly,clearlinux/folly,tomhughes/folly,loversInJapan/folly,rklabs/folly,hongliangzhao/folly,rklabs/folly,loversInJapan/folly,KSreeHarsha/folly,PoisonBOx/folly,ykarlsbrun/folly,CJstar/folly,project-zerus/folly,sonnyhu/folly,charsyam/folly,romange/folly,juniway/folly,ykarlsbrun/folly,sonnyhu/folly,nickhen/folly,mqeizi/folly,romange/folly,bikong2/folly,constantine001/folly,ykarlsbrun/folly,theiver9827/folly,floxard/folly,KSreeHarsha/folly,colemancda/folly,hongliangzhao/folly,zhiweicai/folly,mqeizi/folly,lifei/folly,theiver9827/folly,alexst07/folly,shaobz/folly,nickhen/folly,leolujuyi/folly,xzmagic/folly,facebook/folly,raphaelamorim/folly,SammyK/folly,clearlinux/folly