Add pprof support with HTTP

[szibis]

Heap profile example:

go tool pprof http://localhost:8080/debug/pprof/heap

Or to look at a 30-second CPU profile example:

go tool pprof http://localhost:8080/debug/pprof/profile

Goroutine blocking profile example:

go tool pprof http://localhost:6060/debug/pprof/block

For longer profiling and saving Graphviz in png/svg/pdf:

go tool pprof http://localhost:8080/debug/pprof/profile?seconds=180
Fetching profile from http://localhost:8080/debug/pprof/profile?seconds=180
Please wait... (3m0s)
Saved profile in /tmp/pprof/pprof.statsrelay.localhost:8080.samples.cpu.007.pb.gz
Entering interactive mode (type "help" for commands)
(pprof) top
19890ms of 37300ms total (53.32%)
Dropped 343 nodes (cum <= 186.50ms)
Showing top 10 nodes out of 176 (cum >= 1860ms)
      flat  flat%   sum%        cum   cum%
    9880ms 26.49% 26.49%    10570ms 28.34%  syscall.Syscall
    3130ms  8.39% 34.88%     3130ms  8.39%  runtime.futex
    1320ms  3.54% 38.42%     2590ms  6.94%  runtime.mallocgc
    1180ms  3.16% 41.58%     1180ms  3.16%  syscall.RawSyscall
    1020ms  2.73% 44.32%     1020ms  2.73%  runtime._ExternalCode
    1020ms  2.73% 47.05%     1020ms  2.73%  runtime.epollctl
     970ms  2.60% 49.65%      970ms  2.60%  runtime.epollwait
     570ms  1.53% 51.18%      570ms  1.53%  runtime.heapBitsSetType
     430ms  1.15% 52.33%      430ms  1.15%  runtime.memmove
     370ms  0.99% 53.32%     1860ms  4.99%  runtime.newobject
(pprof) png > graph.png
Generating report in graph.png
(pprof) svg > graph.svg                                                                                                                                                                                                                      Generating report in graph.svg

[szibis]

I was able to generate flame-graph from pprof data in couple of minutes which is very useful.

[jjneely]

Yeah, just merging. :-)

Thank you for your work and contributions.