Before this fix, all existing suites would get wastefully initialized in each subprocess.

Bug: v8:6375
Change-Id: I68d961cde143754724735aecbac605852f89c7d9
Reviewed-on: https://chromium-review.googlesource.com/500187Reviewed-by: Jakob Kummerow <jkummerow@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#45188}