Fixes to roll_chromium_deps.py. Includes the new sheriff email alias, and also fixes to the Clang version detection. The new version checks the CopyBara mirror to find the real clang rev ANGLE ends up with. Bug: angleproject:5926 Change-Id: Ie70319feeb5eefbfba8a6b6d2d57110273d6c3e5 Reviewed-on: https://chromium-review.googlesource.com/c/angle/angle/+/2872070 Commit-Queue: Jamie Madill <jmadill@chromium.org> Reviewed-by: Yuly Novikov <ynovikov@chromium.org>