added a missing hook to IndexedMemPool's testing harness
added a missing hook to IndexedMemPool's testing harness

Summary: IndexedMemPool had one bare usage of std::atomic, rather than
the templated type Atom.  This doesn't affect any non-testing template
instantiations, because those two are usually synonyms, but it could cause
spurious failures of DeterministicSchedule tests.  Found via inspection,
not via failed tests.

Reviewed By: @yfeldblum

Differential Revision: D2277424

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