Always spend 1ms per iteration.

Previously if the profilerthread took a long time to start up then we
would skip through iterations and potentially not gather enough samples.

This forces each iteration to take 1ms.

Bug: v8:10996
Change-Id: I0dd7bb7e31636c9ebf5dd99110c8a976cbc8f045
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2461727
Commit-Queue: Peter Marshall <petermarshall@chromium.org>
Reviewed-by: Simon Zünd <szuend@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70466}