This is a reland of 98cc9e86
Original change's description:
> [test] Creating command before execution phase.
> 
> Immutable command class with shell, flags and
> environment.
> 
> Command creation moved from worker to the main
> process. Because of that there is no need to send
> test cases beyond process boundaries and load test
> suites in worker processes.
> 
> Bug: v8:6917
> Change-Id: Ib6a44278095b4f7141eb9b96802fe3e8117678a6
> Reviewed-on: https://chromium-review.googlesource.com/791710
> Commit-Queue: Michał Majewski <majeski@google.com>
> Reviewed-by: Michael Achenbach <machenbach@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#49746}

Bug: v8:6917
Change-Id: I49c29a8db813c47909f2cc45070ac7721a447c7a
Reviewed-on: https://chromium-review.googlesource.com/800370Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Michał Majewski <majeski@google.com>
Cr-Commit-Position: refs/heads/master@{#49756}