I think this should be added here:

https://cs.chromium.org/chromium/infra/go/src/infra/tricium/appengine/common/swarming.go?l=104

	res, err := swarmingService.Tasks.New(&swarming.SwarmingRpcsNewTaskRequest{
		Name:           "tricium:" + worker.Name,
		Priority:       100,
		ExpirationSecs: 21600,
		Properties:     props,
		PubsubTopic:    pubsubTopic,
		PubsubUserdata: pubsubUserdata,
	}).Do()

should change to something like:

	res, err := swarmingService.Tasks.New(&swarming.SwarmingRpcsNewTaskRequest{
		Name:           "tricium:" + worker.Name,
		Priority:       100,
		ExpirationSecs: 21600,
		Properties:     props,
		PubsubTopic:    pubsubTopic,
		PubsubUserdata: pubsubUserdata,
                Tags:           []string{"gerrit:<ref>", "tricium:1"},
	}).Do()

What might the gerrit <ref> be? Something like "refs/changes/10/12310/1"? What would that be used for?
Also, would we want to include "project:<project-name>"?

It's used to see tasks in https://chromium-swarm.appspot.com/tasklist. We'll want to include as much metadata as possible.

So I'd like the gerrit project name, change ID (e.g. 12310 in your example) but also another tag to uniquely identify the patchset (refs/changes/10/12310/1 would be fine).

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/d032ceda41e95307c49a967cf068f2449740f248

commit d032ceda41e95307c49a967cf068f2449740f248
Author: Quinten Yearsley <qyearsley@chromium.org>
Date: Thu Apr 05 16:15:15 2018

Add tags to swarming tasks for Tricium tasks

This CL would add the tags to tasks triggered by Tricium:
  tricium:1 (for all Tricium tasks)
  function (function name, e.g. GitFileIsolator)
  platform (worker platform, UBUNTU, FUSCHIA, etc.)
and if applicable:
  gerrit_project (e.g. infra/infra)
  gerrit_change (gerrit change ID of the form project~ref~Change-Id-footer)
  gerrit_revision (gerrit change ref of the form refs/changes/23/123/1)

This changes the swarming.go Trigger function to take a tags string,
and constructs the tags string in rpc_trigger, since Trigger doesn't
know any details of the Tricium run (e.g. analyzer, run info), but
the Trigger rpc handler does.

Bug:  805553 
Change-Id: Iaee465be324a076fcbdd94d00094ee4a88f51b4c
Reviewed-on: https://chromium-review.googlesource.com/956485
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>

[modify] https://crrev.com/d032ceda41e95307c49a967cf068f2449740f248/go/src/infra/tricium/appengine/driver/driver.infra_testing
[modify] https://crrev.com/d032ceda41e95307c49a967cf068f2449740f248/go/src/infra/tricium/appengine/driver/rpc_collect_test.go
[modify] https://crrev.com/d032ceda41e95307c49a967cf068f2449740f248/go/src/infra/tricium/appengine/driver/rpc_trigger.go
[modify] https://crrev.com/d032ceda41e95307c49a967cf068f2449740f248/go/src/infra/tricium/appengine/common/swarming.go
[modify] https://crrev.com/d032ceda41e95307c49a967cf068f2449740f248/go/src/infra/tricium/appengine/driver/rpc_trigger_test.go

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/9af405c99dc1dc62d7c79c5baa557f56039d8d50

commit 9af405c99dc1dc62d7c79c5baa557f56039d8d50
Author: Quinten Yearsley <qyearsley@chromium.org>
Date: Wed Apr 25 21:45:48 2018

Extract and use helper functions related to revision refs

In this CL:
 - Extract functions related to revision ref strings to common place
 - (Minor behavior change) In the function for composing gerrit URLs
   return an string when revision ref string is invalid
 - In swarming tags, use CL number and patch set rather than ref string

Using CL number and patch set number was suggested in
https://crrev.com/c/956485.

This CL extracts these to the "common" package because (1) they are
used by multiple other packages, and (2) putting it in the "gerrit"
package and importing the gerrit package from other packages doesn't
work now; due to the way that routes are set up in init.go, each
different app engine module must be isolated in its own package
and not directly use anything from any other module package.

Bug:  805553 
Change-Id: I1ebbabec9910b0cec9e6f5f027ebb4efd655b72c
Reviewed-on: https://chromium-review.googlesource.com/998492
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Commit-Queue: Quinten Yearsley <qyearsley@chromium.org>

[modify] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/gerrit/gerrit_test.go
[modify] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/gerrit/gerrit.infra_testing
[add] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/common/gerrit_helpers.go
[add] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/common/gerrit_helpers_test.go
[modify] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/driver/rpc_trigger_test.go
[modify] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/frontend/run_test.go
[modify] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/driver/rpc_trigger.go
[modify] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/frontend/run.go
[modify] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/gerrit/gerrit.go
[modify] https://crrev.com/9af405c99dc1dc62d7c79c5baa557f56039d8d50/go/src/infra/tricium/appengine/common/common.infra_testing