Signal a condition variable when profiling thread shutdown should occur,
waking up a profiling thread that's currently waiting for the next tick.

Mitigates the case where if a high sample interval is specified (e.g.
60s), the main thread is blocked until the next sample occurs due to a
Sleep() call.

Bug: v8:8843
Change-Id: Ied6b0bfb5c47a072ade17870911b961f5091f613
Reviewed-on: https://chromium-review.googlesource.com/c/1470953
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Alexei Filippov <alph@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59648}