So far we operated under the assumption that only a small number of
modules is being created (and live) at a time, typically just one.
Recently we saw webpages that create multiple modules at the same time.
These counters should give us more insight into the typical number of
modules in the wild.

R=ecmziegler@chromium.org
CC=jwd@chromium.org

Bug: chromium:1076767
Change-Id: I81f657ee76ea155f0df2a5828e6b0f686a7ce7d0
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2182376Reviewed-by: Emanuel Ziegler <ecmziegler@chromium.org>
Commit-Queue: Clemens Backes <clemensb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#67589}