This is a reland of 1d493d31

Original change's description:
> [foozzie] Refactor command abstraction
> 
> This moves code for running d8 into its own class. No functional
> changes intended.
> 
> No-Try: true
> Bug: chromium:1023091
> Change-Id: I7cbfeebd2911dc758322f89cf93666550f2956d9
> Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1906378
> Commit-Queue: Michael Achenbach <machenbach@chromium.org>
> Reviewed-by: Tamer Tas <tmrts@chromium.org>
> Cr-Commit-Position: refs/heads/master@{#64928}

Bug: chromium:1023091
Change-Id: I7df6e12084e20510a400ce209827c2bba8325f86
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/1914209Reviewed-by: Tamer Tas <tmrts@chromium.org>
Commit-Queue: Michael Achenbach <machenbach@chromium.org>
Cr-Commit-Position: refs/heads/master@{#64966}