Inspired by bsuite/compare-baseline.py and tools/perf-to-html.py. The main difference
from the latter is that the new script does not require json files preprocessing and it
is able to compare multiple json files at once (just like bsuite/compare-baseline.py).

This CL also makes tools/run_perf.py relative path friendly.

BUG=

Change-Id: I7be796fa920f8360703806f32767b992eec0f9c2
Reviewed-on: https://chromium-review.googlesource.com/456286Reviewed-by: Michael Stanton <mvstanton@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Commit-Queue: Igor Sheludko <ishell@chromium.org>
Cr-Commit-Position: refs/heads/master@{#43982}