To pickup support for generating tricium config and introducing
mode_allowlist

R=qyearsley, tandrii

Bug: 1194244
Change-Id: I16a8792e8d4df4127c1d545dca246058c8f93066
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/tools/depot_tools/+/2856909Reviewed-by: Andrii Shyshkalov <tandrii@google.com>
Commit-Queue: Yiwei Zhang <yiwzhang@google.com>