pprof support

[mikekap]

This may be a bit of a stretch, but it would be really nice if honest-profiler could output pprof format: https://github.com/google/pprof. pprof has pretty good tools for exploration of sampled stacks.

The actual format pprof expects is a protocol buffer serialized to disk: https://github.com/google/pprof/blob/master/proto/profile.proto . It's pretty easy to fill out for basic usability. I'm not 100% sure where to begin doing this in honest profiler so instead I'm opening this issue.