Change XHProf output format
Change XHProf output format

Summary: Currently the output from `--xprofile` is in compatible with the XHProf application. Specifically, the XHProf application expects JSON encoded data.

Test Plan:
# Ran a command with `--xprofile=profile.json`.
# Uploaded the profile via `arc upload xprofile.json`.
# Retried the PHID of the uploaded file with `echo '{"names": ["Fxxx"]}' | arc call-conduit phid.lookup`.
# Went to `/xhprof/profile/PHID-FILE-xxxxxxxxxxxxxxxxxxxx` and saw the profile.

Reviewers: epriestley, #blessed_reviewers

Reviewed By: epriestley, #blessed_reviewers

Subscribers: Korvin, epriestley

Differential Revision: https://secure.phabricator.com/D12514

julkiewicz/libphutil,julkiewicz/libphutil,julkiewicz/libphutil