The plan is to do this with a Gerrit plugin that uses a plugin endpoint to add a button element to each robot comment: https://gerrit-review.googlesource.com/c/gerrit/+/146790

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/gerrit-plugins/tricium/+/3b01e924a27201d6f0e43247530c8cdf00d7b7b7

commit 3b01e924a27201d6f0e43247530c8cdf00d7b7b7
Author: Quinten Yearsley <qyearsley@chromium.org>
Date: Mon Feb 05 20:57:59 2018

Add tricium-feedback-button element to existing tricium plugin

This CL adds a custom element tricium-feedback-button,
which would send a "not useful" feedback report to the
Tricium service. The particular Tricium service to send
the report to is determined by the project-specific
plugin config.

Bug:  784368 
Change-Id: I8dd158b2b1f7c92291ddb5134994d0957b9e9594
Reviewed-on: https://chromium-review.googlesource.com/849636
Reviewed-by: Marc-Antoine Ruel <maruel@chromium.org>
Reviewed-by: Emma Söderberg <emso@chromium.org>

[modify] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/src/main/resources/static/tricium.js
[modify] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/src/main/resources/static/tricium-client.js
[add] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/src/main/resources/static/tricium-feedback-button.js
[add] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/src/main/resources/static/tricium-feedback-button.html
[modify] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/src/main/resources/static/tricium-view.js
[modify] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/test/tricium-client_test.html
[modify] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/test/tricium-view_test.html
[add] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/test/tricium-feedback-button_test.html
[modify] https://crrev.com/3b01e924a27201d6f0e43247530c8cdf00d7b7b7/test/index.html

One thought: It's possible that we may want to have a way to hide a comment after it has been reported as "not useful".

It should *almost* become hidden but I'd say not *completely* hidden, just so that if a user misclicks the button, they still have a chance to revert the click.

Which also means the API needs a way to revert the "not useful" click.

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/gerrit-plugins/tricium/+/17c19db30fd1149e3ace6c8cf3bc96a3b073fb76

commit 17c19db30fd1149e3ace6c8cf3bc96a3b073fb76
Author: Quinten Yearsley <qyearsley@chromium.org>
Date: Tue Feb 20 20:36:58 2018

Change feedback button style to match "please fix" button

Bug:  784368 
Change-Id: Ic3c27929cd172cf1c91abc0fbdfa111b265f234b
Reviewed-on: https://chromium-review.googlesource.com/926965
Reviewed-by: Aaron Gable <agable@chromium.org>

[modify] https://crrev.com/17c19db30fd1149e3ace6c8cf3bc96a3b073fb76/src/main/resources/static/tricium-feedback-button.html

I've now tested the "not useful" button and confirmed that it sends a ReportNotUseful request to Tricium -- BUT, it doesn't give any indication that it has done so.

Next to do: give some indication that the request has succeeded, and ideally provide an "undo" button. I should see what critique does.

The following revision refers to this bug:
  https://chromium.googlesource.com/infra/gerrit-plugins/tricium/+/92f169b4ab4638aa68c1c016fc8eb470327d63a3

commit 92f169b4ab4638aa68c1c016fc8eb470327d63a3
Author: Quinten Yearsley <qyearsley@chromium.org>
Date: Fri Mar 02 20:17:21 2018

After sending "not useful", disable button and change text

Bug:  784368 
Change-Id: I055d43a370805b19db7198d23a911ff14e252986
Reviewed-on: https://chromium-review.googlesource.com/941969
Reviewed-by: Aaron Gable <agable@chromium.org>

[modify] https://crrev.com/92f169b4ab4638aa68c1c016fc8eb470327d63a3/src/main/resources/static/tricium-feedback-button.html
[modify] https://crrev.com/92f169b4ab4638aa68c1c016fc8eb470327d63a3/test/tricium-feedback-button_test.html
[modify] https://crrev.com/92f169b4ab4638aa68c1c016fc8eb470327d63a3/src/main/resources/static/tricium-feedback-button.js

This is technically "done", but it might be nice to keep this open until we have better tracking/monitoring/visualization of "not useful" metrics.

Note, I just verified that "not useful" works in the infra repo (on this CL: https://chromium-review.googlesource.com/c/infra/infra/+/965023/1)

The current way to track "not useful" feedback is via Feedback RPC requests:
https://tricium-dev.appspot.com/rpcexplorer/services/tricium.Tricium/Feedback

I think we should close this bug whenever we have something good enough to put in a demo (something to put at go/tricium-milestone-feedback-try).

Marc-Antoine, do you think it would be OK to send out such a demo now? Perhaps after adding a web UI for viewing current "not useful" counts?

Yes (sorry for the delay)

Returning this bug to what it was before and making a separate issue for the task of surfacing these numbers in a web UI: bug 845530