Indeed, CQ has posted the following message on the CL:
>> only full committers or CL owner with tryjob access are allowed to trigger CQ

That's a good question, but I think we need to ask CQ owners about this. Thus, moving this issue to Chromium to be able to assign correct component.

Moved issue v8:7913 to now be  issue chromium:859498 .

And marking Untriaged to have it triaged by Foundation team.

This was a bit different in Rietveld, but current state is here since Gerrit migration in Feb 2017. See http://go/gerrit-cq-for-contributors which explains this in detail. This may be especially useful: https://bugs.chromium.org/p/chromium/issues/detail?id=692611#c5

Yea, this is WAI. If the contributor has no trybot access, someone else must land the CL for them.

But regular contributors can just request trybot access...

Re #7: Where does a contributor request try-bot access? We should add this important piece of information to https://github.com/v8/v8/wiki/Contributing. 

Chromium has a dedicated process for try-job-access here:
https://www.chromium.org/getting-involved/become-a-committer

Maybe we could mimic that?

Anybody that has Chromium tryjob access has automatic access to V8 too. But not the other way around. So we'd need a process for sole V8 contributors that are not committers.

The easiest way might be to simply use the Chromium process anyway?