Labels and aggregation: "average"

[petethepig]

There's currently this problem that when you upload a pprof profile with aggregation=average and labels inside pprof it creates multiple writes to the storage and as a consequence, when you later make a query the denominator is incorrect. For example, if you have one pprof file with 3 labelsets, denominator becomes 3, when it should be 1.

goroutines is currently the only type that as this issue afaik.