"the try bot picker UI in polygerrit" did you mean Rietveld here? because PG does not have a trybot UI yet, it will be added soonish in https://bugs.chromium.org/p/chromium/issues/detail?id=618023

Yes, sorry. I was thinking of the UI in rietvield. I'm assuming the UI in polygerrit would be similar or better :)

Yes I think it will be similar. So to clarify: This feature request is to have a similar UI for selecting trybots to add to the 'CQ_INCLUDE_TRYBOTS' keyword?

Yes. Though I don't particularly care that it uses the CQ_INCLUDE_TRYBOTS keyword as the mechanism to add the selected try bots to the cq set. 

If this was Rietveld I would say we cannot do it because of adding complexity to an already very complex codebase. But since this is for Gerrit we could in theory write our own plugin to allow picking extra bots.
Will take a look at this sometime after the trybot UI is available to see how hard it is to do and if the effort is worth the benefit.

sgtm

Moved issue skia:5948 to now be issue chromium:845884.

We could add a checkbox in the buildbucket plugin that says something like:
"Add to CQ_INCLUDE_TRYBOTS in description"
The plugin would then need to edit the change description to add CQ_INCLUDE_TRYBOTS or modify the existing CQ_INCLUDE_TRYBOTS line to include the new bots.

or some other idea...

Do I understand correctly that the goal is to tell CQ extra builders that must pass? CQ_INCLUDE_TRYBOTS is a human-oriented way of telling CQ what to do. FWIU the proposal here is to use human-oriented medium for service-to-service (buildbucket->CQ) communication. +tandrii, CQ owner, for more ideas.

Since CQ has today no persistent state for a CL outside of Gerrit itself, there is no other place to record the additional builders. So, either a special comment and/or CQ-Include-Trybots: footer are required. Hence, idea in #8 is the best one.

In a dream world, CQ has its own GAE app. It can keep track of what builders are additionally required for a CL and implements this API: 

  update_extra_builders(cl, add_builders, rem_builders)
  get_state(cl, revision=None) => {
    extra_builders: [...]
    default: [...]  # from cq.cfg,
    ...,
  }