Added /infra with chrome-infra specific files.
/infra/project-config/cr-buildbucket.cfg defines v8 buckets on cr-buildbucket.appspot.com

R=tandrii@chromium.org, machenbach@chromium.org, sergiyb@chromium.org
BUG=

Review URL: https://codereview.chromium.org/1161143002

Cr-Commit-Position: refs/heads/master@{#28736}