Permit individual calls to CpuProfiler::StartSampling to provide their
own requested sampling interval, to be snapped to the profiler's
sampling interval. Use the greatest common divisor of all sample rates
to determine what sample rate should be chosen for the sampling thread,
and dispatch samples to attached profilers based on their requested
sample periodicity.

Change-Id: I0b076d09761d7176f31725e112578b68ab5da54c
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1484461Reviewed-by: Ulan Degenbaev <ulan@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Commit-Queue: Andrew Comminos <acomminos@fb.com>
Cr-Commit-Position: refs/heads/master@{#61548}