A CL for this landed:
https://chromium-review.googlesource.com/c/infra/luci/recipes-py/+/701501

We will likely use scheduler module [1] to trigger builds because buildbucket is not able to merge build requests together. Example how Chromium CI was converted from buildbucket to scheduler: https://crrev.com/c/898505.

[1]: https://chromium.googlesource.com/infra/luci/recipes-py/+/master/recipe_modules/scheduler/api.py

P.S. For those few builders that do not want to merge builds, we'll use buildbucket.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/tools/build/+/e78d0ebc8d89d79154dc0cafe588ec255c6be2cc

commit e78d0ebc8d89d79154dc0cafe588ec255c6be2cc
Author: Sergiy Byelozyorov <sergiyb@chromium.org>
Date: Mon Apr 02 17:00:13 2018

[V8] Trigger child builders using scheduler module on LUCI

TBR=machenbach@chromium.org

Bug:  773297 
Change-Id: I8ebf77a5b611bc41beaa717d3f6d68d68f590d2d
Reviewed-on: https://chromium-review.googlesource.com/989713
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>

[modify] https://crrev.com/e78d0ebc8d89d79154dc0cafe588ec255c6be2cc/scripts/slave/README.recipes.md
[add] https://crrev.com/e78d0ebc8d89d79154dc0cafe588ec255c6be2cc/scripts/slave/recipes/v8.expected/full_client_v8_V8_Linux___builder_trigger_on_luci.json
[modify] https://crrev.com/e78d0ebc8d89d79154dc0cafe588ec255c6be2cc/scripts/slave/recipe_modules/v8/api.py
[modify] https://crrev.com/e78d0ebc8d89d79154dc0cafe588ec255c6be2cc/scripts/slave/recipe_modules/v8/__init__.py
[modify] https://crrev.com/e78d0ebc8d89d79154dc0cafe588ec255c6be2cc/scripts/slave/recipes/v8.py

The following revision refers to this bug:
  https://chromium.googlesource.com/v8/v8.git/+/cb60b0daf730f2585dcff80e2f93c2b87e2fd456

commit cb60b0daf730f2585dcff80e2f93c2b87e2fd456
Author: Sergiy Byelozyorov <sergiyb@chromium.org>
Date: Mon Apr 02 18:42:06 2018

[tools] Whitespace CL

TBR=sergiyb@chromium.org

Bug:  chromium:773297 
Change-Id: I51a9cff42adb477bc089a869741e34513426e5b6
Reviewed-on: https://chromium-review.googlesource.com/989715
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52312}
[modify] https://crrev.com/cb60b0daf730f2585dcff80e2f93c2b87e2fd456/tools/whitespace.txt

Update: this has been implemented, but permissions need to be fixed: https://ci.chromium.org/p/v8/builders/luci.v8.ci/V8%20Linux64%20-%20builder/420.

Android, would you happen to know which permission do I need to add and where to fix the above failure?

s/Android/Andrii/

Have you granted TRIGGERER permission to task service account of your CI bots?
See chromium's config for inspiration: https://cs.chromium.org/chromium/src/infra/config/global/luci-scheduler.cfg?q=luci-scheduler.cfg&sq=package:chromium&dr&l=28

Nice. Thanks. Done the same for V8.

The following revision refers to this bug:
  https://chromium.googlesource.com/v8/v8.git/+/80d587d7ea395004f068610282da2aecc360c60b

commit 80d587d7ea395004f068610282da2aecc360c60b
Author: Sergiy Byelozyorov <sergiyb@chromium.org>
Date: Tue Apr 03 14:24:26 2018

[tools] Whitespace CL

TBR=sergiyb@chromium.org

Bug:  chromium:773297 
Change-Id: Icbff53ed84b72d74f1db9884b3b846b8ff72686b
No-Try: true
No-Presubmit: true
Reviewed-on: https://chromium-review.googlesource.com/992317
Reviewed-by: Sergiy Byelozyorov <sergiyb@chromium.org>
Commit-Queue: Sergiy Byelozyorov <sergiyb@chromium.org>
Cr-Commit-Position: refs/heads/master@{#52326}
[modify] https://crrev.com/80d587d7ea395004f068610282da2aecc360c60b/tools/whitespace.txt

This has been completed, although we'll still need to migrate all scheduler configs from masters to luci-scheduler.cfg, but this will be done on a per-builder basis as part of the issue 793687. Note that only LUCI builds are using luci-scheduler since it does not copy the list of changes like api.trigger does and Buildbot UI is not able to display list of changes based on buildset revision.