Some thoughts:

I'm not sure if it really belongs with the plugin config, since it seems like a detail that's not necessarily related to the plugin, and this mapping is already in the service config.

Looking up the corresponding tricium project in the service config may incur a minor performance penalty since it might involve fetching the config and iterating through projects. But, this may not be a significant performance issue if the mapping is cached somehow -- perhaps stored in datastore?

What do you think?

I think that makes sense. We could add the basic service config lookup and then optimize if needed later.

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/infra/+/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97

commit e05e0bd3d6cadc75a606860e0cd46705c2ac8f97
Author: Emma <emso@chromium.org>
Date: Tue Nov 21 08:49:52 2017

Cleans up Gerrit project mapping.

- Sends the right project name in the analyze request.
- Tracks the gerrit project name.

Bug:785180
Change-Id: I4582b29738b91e760b16842b7210772b83e0bf18
Reviewed-on: https://chromium-review.googlesource.com/774618
Commit-Queue: Emma Söderberg <emso@chromium.org>
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Reviewed-by: Quinten Yearsley <qyearsley@chromium.org>

[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/common/track/track.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/gerrit/gerrit_test.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/api/v1/tricium.pb.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/frontend/rpc_analyze_test.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/gerrit/poll.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/frontend/gerrit.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/devcfg/services/tricium-dev/service.cfg
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/api/v1/config.proto
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/api/v1/pb.discovery.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/frontend/rpc_progress.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/api/v1/config.pb.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/gerrit/gerrit.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/api/v1/tricium.proto
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/tricium/appengine/frontend/rpc_analyze.go
[modify] https://crrev.com/e05e0bd3d6cadc75a606860e0cd46705c2ac8f97/go/src/infra/appengine/test-results/frontend/event_logging_test.go

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/gerrit-plugins/tricium/+/6b9b8a49dc3444a63d0569245b1940d0bb84456a

commit 6b9b8a49dc3444a63d0569245b1940d0bb84456a
Author: Quinten Yearsley <qyearsley@chromium.org>
Date: Tue Nov 21 21:56:32 2017

Tricium plugin: send Gerrit host with Progress request

This is the plugin-side change related to https://crrev.com/c/774618.

Bug:  785180 
Change-Id: I2cd21397bb6ada6fc9bee6cbf92670e4f4ac280c
Reviewed-on: https://chromium-review.googlesource.com/777223
Reviewed-by: Nodir Turakulov <nodir@chromium.org>
Reviewed-by: Emma Söderberg <emso@chromium.org>

[modify] https://crrev.com/6b9b8a49dc3444a63d0569245b1940d0bb84456a/src/main/resources/static/tricium-client.js