It's missing from one of the Mojo interface manifests, because I didn't know those existed when I implemented it and nothing broke other than the error message you're seeing.

I'll take this bug and fix it.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/f982545ca8ee348c0a8c7076406543ba05fe5598

commit f982545ca8ee348c0a8c7076406543ba05fe5598
Author: Julia Tuttle <juliatuttle@chromium.org>
Date: Tue Nov 21 15:24:05 2017

Add ReportingServiceProxy to content_browser Mojo manifest.

Bug:  784518 
Change-Id: I7f0f75fdf24be675ece8f83bcf0d3447ffc88258
Reviewed-on: https://chromium-review.googlesource.com/779245
Reviewed-by: Daniel Cheng <dcheng@chromium.org>
Commit-Queue: Julia Tuttle <juliatuttle@chromium.org>
Cr-Commit-Position: refs/heads/master@{#518256}
[modify] https://crrev.com/f982545ca8ee348c0a8c7076406543ba05fe5598/content/public/app/mojo/content_browser_manifest.json

Even though r518256 landed in 64.0.3275.0, dev channel is at 64.0.3278.0 and I'm still seeing the message.

The CL added content::mojom::ReportingServiceProxy to the manifest, but the interface is named blink::mojom::ReportingServiceProxy.

And note that interfaces missing from the spec can't really fail in a more visible way because it is not something we want to e.g. DCHECK against.

Ideally there would be at least one browser or layout test that covers the need for this interface to be connected properly.

Augh. Okay, thanks.

OK, so both blink::mojom::ReportingServiceProxy and content::mojom::ReportingServiceProxy are in content/public/app/mojo/content_browser_manifest.json in the same section. Still seeing the message with my ToT build.

This is now because the renderer is requesting the interfacing from its
frame host (which applies a different interface filter) rather than
directly from the browser process (which has the correct filter and
actually has the implementation wired in).

This code:
https://cs.chromium.org/chromium/src/third_party/WebKit/Source/core/frame/Intervention.cpp?rcl=faa974734a75c2fc4b855f2b67afda7f2aa4efe0&l=47

should be:

Platform* platform = Platform::Current();
platform->GetConnector()->BindInterface(
    platform->GetBrowserServiceName(), &service);

thestig, I'm gonna write up a CL to fix this and send it to you for review.

Oh, sounds like it's already fixed. thestig, is this working for you yet?

Still seeing the message at r522488.

It's definitely not already fixed. I'm pretty sure https://chromium-review.googlesource.com/c/chromium/src/+/806477 does fix it though. Anything blocking that from landing?

Oh... still waiting on an OWNER to review...

I applied the CL locally and it fixes it for me.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/0ae35e181947085b6b235809244ecbc14b0ac802

commit 0ae35e181947085b6b235809244ecbc14b0ac802
Author: Julia Tuttle <juliatuttle@chromium.org>
Date: Fri Dec 08 18:21:10 2017

Reporting API: Fix some Blink plumbing.

TBR=paulmeyer@chromium.org

Bug:  784518 
Change-Id: I5127e19ebd1d3490713e586437d32d46e402c404
Reviewed-on: https://chromium-review.googlesource.com/806477
Commit-Queue: Julia Tuttle <juliatuttle@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Commit-Position: refs/heads/master@{#522821}
[modify] https://crrev.com/0ae35e181947085b6b235809244ecbc14b0ac802/third_party/WebKit/LayoutTests/reporting-observer/reporting-api.html
[modify] https://crrev.com/0ae35e181947085b6b235809244ecbc14b0ac802/third_party/WebKit/Source/core/frame/Deprecation.cpp
[modify] https://crrev.com/0ae35e181947085b6b235809244ecbc14b0ac802/third_party/WebKit/Source/core/frame/Intervention.cpp

This also fixes the issue for me. Can you merge to M64? Thanks.

(FYI: You may need to merge e5df6cff first, or merge manually to resolve conflicts).

Your change meets the bar and is auto-approved for M64. Please go ahead and merge the CL to branch 3282 manually. Please contact milestone owner if you have questions.
Owners: cmasso@(Android), cmasso@(iOS), kbleicher@(ChromeOS), abdulsyed@(Desktop)

For more details visit https://www.chromium.org/issue-tracking/autotriage - Your friendly Sheriffbot

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/bcfa50fe2abe66e73d099a12ca23108916df5ffe

commit bcfa50fe2abe66e73d099a12ca23108916df5ffe
Author: Julia Tuttle <juliatuttle@chromium.org>
Date: Mon Dec 11 22:20:28 2017

Reporting API: Fix some Blink plumbing.

TBR=juliatuttle@chromium.org, paulmeyer@chromium.org

(cherry picked from commit 71cb4f6e0a6b6bcf19fef0738ceda34fa4a2b2e9)

Bug:  784518 
Change-Id: I5127e19ebd1d3490713e586437d32d46e402c404
Reviewed-on: https://chromium-review.googlesource.com/806477
Commit-Queue: Julia Tuttle <juliatuttle@chromium.org>
Reviewed-by: Ken Rockot <rockot@chromium.org>
Cr-Original-Commit-Position: refs/heads/master@{#522821}
Reviewed-on: https://chromium-review.googlesource.com/820850
Reviewed-by: Julia Tuttle <juliatuttle@chromium.org>
Cr-Commit-Position: refs/branch-heads/3282@{#152}
Cr-Branched-From: 5fdc0fab22ce7efd32532ee989b223fa12f8171e-refs/heads/master@{#520840}
[modify] https://crrev.com/bcfa50fe2abe66e73d099a12ca23108916df5ffe/third_party/WebKit/LayoutTests/reporting-observer/reporting-api.html
[modify] https://crrev.com/bcfa50fe2abe66e73d099a12ca23108916df5ffe/third_party/WebKit/Source/core/frame/Deprecation.cpp
[modify] https://crrev.com/bcfa50fe2abe66e73d099a12ca23108916df5ffe/third_party/WebKit/Source/core/frame/Intervention.cpp