This method only recorded stats of the generated code object. Since
both counters that are updated are thread-safe anyway, we can just
update them from the background instead (during {ExecuteCompilation}).

R=mstarzinger@chromium.org

Bug: v8:7921
Change-Id: Ia6074be8339b100f328938136ecb10144fc79f12
Reviewed-on: https://chromium-review.googlesource.com/c/1291074
Commit-Queue: Clemens Hammacher <clemensh@chromium.org>
Reviewed-by: Michael Starzinger <mstarzinger@chromium.org>
Cr-Commit-Position: refs/heads/master@{#56827}