Should make the process of rolling Chromium DEPS into ANGLE easier.
Eventually we could set up an auto-roller.

Original:

https://webrtc.googlesource.com/src/+/master/tools_webrtc/autoroller/roll_deps.py

Modified to include ANGLE's Chromium DEPS only. We will continue to use
Skia's auto-roller for more one-off DEPS.

Also adds a 'chromium_revision' DEPS custom variable that we could
potentially use for other things like pinning a Chromium version on our
testers.

Sample usage:

python scripts/roll_deps.py -v --clean -i

-v : verbose
--clean : cleans previous roll branch
-i : ignore dirty tree

Bug: angleproject:3986
Change-Id: I7289cf76eb5635a286c20453e846d4ff9a0481b1
Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/1852707
Commit-Queue: Jamie Madill <jmadill@chromium.org>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>