runtime: accept NumGC==0 in TestMemStats
runtime: accept NumGC==0 in TestMemStats

TestMemStats currently requires that NumGC != 0, but GC may
legitimately not have run (for example, if this test runs first, or
GOGC is set high, etc). Accept NumGC == 0 and instead sanity check
NumGC by making sure that all pause times after NumGC are 0.

Fixes #11989.

Change-Id: I4203859fbb83292d59a509f2eeb24d6033e7aabc
Reviewed-on: https://go-review.googlesource.com/17830
Run-TryBot: Austin Clements <7ea35d812706d9213868749011af1ed4fa2f6aa0@google.com>
TryBot-Result: Gobot Gobot <66cb808b70d30c07676d5e946fee83fd561249e5@golang.org>
Reviewed-by: Mikio Hara <e2f4d2eec1d9a1f781345cdd7260d7d52e6468ae@gmail.com>

polyverse-security/go,golang/go,vanloswang/go,goodlang/good,ImJasonH/go,momchil-velikov/go,binarycrusader/go,theif519/go,CAFxX/go,codestation/go,codestation/go,vanloswang/go,cyberroadie/go,ImJasonH/go,sndnvaps/go,josharian/go,theif519/go,josharian/go,codestation/go,deft-code/go,4ad/go,mwhudson/go,golang/go,linux-on-ibm-z/go,polyverse-security/go,derekmarcotte/go,miolini/go,cyberroadie/go,vsekhar/elastic-go,Endika/go,polyverse-security/go,mwhudson/go,cloudflare/go,roth1002/go,cyberroadie/go,Samurais/go,Cofyc/go,derekmarcotte/go,nawawi/go,theif519/go,sndnvaps/go,goodlang/good,nawawi/go,ImJasonH/go,vsekhar/elastic-go,binarycrusader/go,akutz/go,Endika/go,roth1002/go,linux-on-ibm-z/go,suncycheng/go,momchil-velikov/go,suncycheng/go,ganboing/go-esx,kim-racktop/go,4ad/go,vanloswang/go,miolini/go,CAFxX/go,binarycrusader/go,miolini/go,vsekhar/elastic-go,Cofyc/go,kim-racktop/go,sndnvaps/go,Endika/go,goodlang/good,ganboing/go-esx,goodlang/good,deft-code/go,suncycheng/go,Samurais/go,deft-code/go,ganboing/go-esx,cloudflare/go,goodlang/good,linux-on-ibm-z/go,sndnvaps/go,Endika/go,4ad/go,akutz/go,binarycrusader/go,linux-on-ibm-z/go,deft-code/go,vanloswang/go,deft-code/go,josharian/go,vanloswang/go,Cofyc/go,codestation/go,miolini/go,mwhudson/go,linux-on-ibm-z/go,Samurais/go,akutz/go,josharian/go,kim-racktop/go,cloudflare/go,binarycrusader/go,momchil-velikov/go,derekmarcotte/go,linux-on-ibm-z/go,Samurais/go,nawawi/go,ganboing/go-esx,kim-racktop/go,Samurais/go,miolini/go,codestation/go,theif519/go,4ad/go,kim-racktop/go,sndnvaps/go,CAFxX/go,golang/go,cloudflare/go,kim-racktop/go,momchil-velikov/go,momchil-velikov/go,vanloswang/go,4ad/go,golang/go,4ad/go,derekmarcotte/go,nawawi/go,roth1002/go,kim-racktop/go,suncycheng/go,CAFxX/go,golang/go,CAFxX/go,cyberroadie/go,deft-code/go,Endika/go,theif519/go,ganboing/go-esx,vsekhar/elastic-go,ImJasonH/go,polyverse-security/go,roth1002/go,vsekhar/elastic-go,cyberroadie/go,ImJasonH/go,momchil-velikov/go,golang/go,mwhudson/go,Cofyc/go,roth1002/go,ImJasonH/go,ganboing/go-esx,josharian/go,Samurais/go,cloudflare/go,goodlang/good,linux-on-ibm-z/go,nawawi/go,akutz/go,Samurais/go,cloudflare/go,goodlang/good,codestation/go,mwhudson/go,binarycrusader/go,derekmarcotte/go,Cofyc/go,linux-on-ibm-z/go,momchil-velikov/go,akutz/go,vsekhar/elastic-go,polyverse-security/go,CAFxX/go,suncycheng/go,deft-code/go,Cofyc/go,miolini/go,polyverse-security/go,suncycheng/go,josharian/go,theif519/go,ImJasonH/go,vanloswang/go,roth1002/go,akutz/go,derekmarcotte/go,codestation/go,sndnvaps/go,4ad/go,Endika/go,mwhudson/go,codestation/go,Samurais/go,josharian/go,derekmarcotte/go,ganboing/go-esx,golang/go,polyverse-security/go,cyberroadie/go,miolini/go,mwhudson/go,nawawi/go,akutz/go,Cofyc/go,cyberroadie/go,derekmarcotte/go,christopher-henderson/Go,miolini/go,binarycrusader/go,akutz/go,Endika/go,nawawi/go,mwhudson/go,sndnvaps/go,roth1002/go,ImJasonH/go,CAFxX/go,vsekhar/elastic-go,roth1002/go,kim-racktop/go,vanloswang/go,theif519/go,suncycheng/go,binarycrusader/go,suncycheng/go,CAFxX/go,cloudflare/go,theif519/go,golang/go,cloudflare/go,ganboing/go-esx,Endika/go,momchil-velikov/go,nawawi/go,goodlang/good,deft-code/go,Cofyc/go,polyverse-security/go,josharian/go,cyberroadie/go,vsekhar/elastic-go,4ad/go,sndnvaps/go