profiling: add statprof support for Chrome trace viewer rendering
We synthesize function call begin/end events from snapshots, and
try (configurably) to eliminate "noisy" stack frames.
Example invocation:
hg --config profiling.output=$HOME/Desktop/clone.json \
--config profiling.statformat=chrome \
--profile clone https://www.mercurial-scm.org/repo/hg
$ hg init
$ touch unknown
$ touch a
$ hg add a
$ hg ci -m "1"
$ touch b
$ hg add b
$ hg ci -m "2"
Should show unknown
$ hg status
? unknown
$ hg revert -r 0 --all
removing b
Should show unknown and b removed
$ hg status
R b
? unknown
Should show a and unknown
$ ls
a
unknown