Add simple log file test with processor.mjs, mostly focusing on parsing
the log file correctly.

Change-Id: Ie8db569b65ecd526ef4474a64d4019f00707d159
Bug: v8:10668
Reviewed-on: https://chromium-review.googlesource.com/c/v8/v8/+/2484515
Commit-Queue: Dan Elphick <delphick@chromium.org>
Auto-Submit: Camillo Bruni <cbruni@chromium.org>
Reviewed-by: Dan Elphick <delphick@chromium.org>
Cr-Commit-Position: refs/heads/master@{#70806}