go/ssa: report memory consumption separated by phase in stdlib_test
go/ssa: report memory consumption separated by phase in stdlib_test

LGTM=gri
R=gri
CC=golang-codereviews
https://golang.org/cl/170600043

josharian/tools,glasser/golang-tools,cmars/tools,sshetty10/tools,magiccao/tools,matryer/tools,matryer/tools,springning/tools,nicot/tools,cw2018/tools,magiccao/tools,runcom/tools,maddyonline/tools,sshetty10/tools,glasser/golang-tools,nicot/tools,4ad/tools,maddyonline/tools,josharian/tools,jdhenke/tools,4ad/tools,syreclabs/go-tools,josharian/tools,syreclabs/go-tools,springning/tools,cw2018/tools,argandas/tools,nicot/tools,nicot/tools,syreclabs/go-tools,argandas/tools,jdhenke/tools,syreclabs/go-tools,golang/tools,magiccao/tools,golang/tools,matryer/tools,josharian/tools,springning/tools,jdhenke/tools,glasser/golang-tools,sshetty10/tools,springning/tools,golang/tools,dmitris/tools,matryer/tools,jdhenke/tools,magiccao/tools,argandas/tools,runcom/tools,sshetty10/tools,cmars/tools,dmitris/tools,syreclabs/go-tools,cw2018/tools,maddyonline/tools,cmars/tools,4ad/tools,runcom/tools,maddyonline/tools,runcom/tools,syreclabs/go-tools,dmitris/tools,golang/tools,golang/tools,dmitris/tools,cw2018/tools,cmars/tools,argandas/tools,glasser/golang-tools