[autoroll] Add gn => Chromium roller
[autoroll] Add gn => Chromium roller

Possible after https://chromium-review.googlesource.com/c/chromium/src/+/2743918

Bug: skia:11712,chromium:1177288
Change-Id: I207aab15f14ca9a320a81467bcadd1451c250b85
Reviewed-on: https://skia-review.googlesource.com/c/buildbot/+/382696
Auto-Submit: Nico Weber <c0f02d98506190746d1cdcb01be0f37b51e27077@chromium.org>
Commit-Queue: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>
Reviewed-by: Eric Boren <0e499112533c8544f0505ea0d08394fb5ad7d8fa@google.com>

google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot,google/skia-buildbot