It looks like this doesn't cover everything and I should use crbug.com/726507 as an example instead.

https://docs.google.com/document/d/1_9SDp_7iIFXF4ASBCdH4JbcftYo6yq1wYS7dnEZce6s/edit provides the list of steps that the LUCI repos used to migrate from github to gerrit last night. Not all of them apply (updating go stuff for example) but basically these are the steps to use:

1) update chromium.googlesource.com/syzygy with the latest content (either via gob-ctl copy configs or via manual force-push)
2) update permissions on syzygy to match chromium/src
3) update infra/config/cq.cfg to add a gerrit cq
3a) update puppet to have the cq start running the new cq
3b) add a buildbucket.cfg listing the trybots syzygy uses
4) update codereview.settings to upload to gerrit by default
5) halt mirroring from github to external/github.com/google/syzygy and mark both the github repo and the googlesource mirror as fully read-only
6) update rietveld to refust uploads to the syzygy project

Does #5 means that we'll have to move away from GitHub and use googlesource instead?

Yes, it does mean that. You can either use GitHub and pull requests, or googlesource and gerrit. You cannot use github with gerrit review. All the other projects (luci, catapult, dart, etc) are going this same route.

Ok, we've decided to move the code to googlesource but we'll keep Github as our landing page (and our wiki will stay there). We'll manually mirror the googlesource project to Github until 529026 get fixed.

Ok, cool. I have the mirroring solution mostly in place (described in blocking bug). Catapult is also blocking on mirroring being working, so I'll do both syzygy and catapult at the same time in early sept after I get back from vacation.

Mirroring is now in place! I'd like to set a migration date of Tuesday, september 26. Does that work for you?

I'm not sure that it'll work for us :(, I'm leaving for Japan next week (for 2 months) so I'll spent 2 days travelling and one packing etc, and I've a summit the week after that (the week post Blink-on).

We're also blocked by crbug.com/759092 at the moment... 

The problem is that there's no more Syzygy team, we do want to keep the project alive because it's still in use (for SyzyAsan) and we sometime have to push some fixes / new features (mostly done by interns) but it's hard for us to justify spending too much time on this... 

How much work do you think that this will require? 

The bottom line is that if we *don't* migrate syzygy on the 26th, it will simply become unreviewable. Rietveld will become read-only and it won't have any configuration in place to make it reviewable via Gerrit, so the only options will be either direct push without review, or making no changes at all.

This migration should require no work on your behalf. I've done this a dozen times already, I know what all the permissions need to be, and I can land all the changes myself.

And while issue 759092 is a big issue, it doesn't block the transition of code review tool. Everything about how post-submit bots check out syzygy will remain the same. And as long as your trybots use bot_update (they do: https://build.chromium.org/p/tryserver.client.syzygy/builders/win_dbg_try/builds/864) then they'll know how to check out syzygy patches as well.

Great, thanks Aaron! 

Actualling going to do this on Wednesday the 27th due to promo committees being on the 26th.

The following revision refers to this bug:
  https://chromium.googlesource.com/syzygy/+/341883a0c6e94db8ff0dabdd69666e6ab23d7ca0

commit 341883a0c6e94db8ff0dabdd69666e6ab23d7ca0
Author: Aaron Gable <agable@chromium.org>
Date: Wed Sep 27 23:01:39 2017

Upload Syzygy changes to Gerrit by default

Bug:  chromium:753912 
Change-Id: I9f0067af6ac9eba49ef84c8098ebb1865b98d37b
Reviewed-on: https://chromium-review.googlesource.com/688737
Reviewed-by: Andrii Shyshkalov <tandrii@chromium.org>

[modify] https://crrev.com/341883a0c6e94db8ff0dabdd69666e6ab23d7ca0/codereview.settings

This is now done! Please update this bug or the PSA thread if any problems are encountered.