Prior langing massive async instrumentation refactoring let's add a perf
test to track our progress.

R=dgozman@chromium.org

Bug: v8:7078
Change-Id: I11e1ec962a9f384c2c778061c48935ac410fbe53
Reviewed-on: https://chromium-review.googlesource.com/766647Reviewed-by: Dmitry Gozman <dgozman@chromium.org>
Reviewed-by: Jakob Gruber <jgruber@chromium.org>
Commit-Queue: Aleksey Kozyatinskiy <kozyatinskiy@chromium.org>
Cr-Commit-Position: refs/heads/master@{#49365}