Update masters after the tryserver split.

Also replace deprecated linux_chromium_rel with linux_chromium_rel_swarming, while I'm at it.

R=agable@chromium.org, maruel@chromium.org
BUG=395196

Review URL: https://codereview.chromium.org/415323002

git-svn-id: https://src.chromium.org/svn/trunk/src/base@285752 4ff67af0-8c30-449e-8e8b-ad334ec8d88c