If is easy to add a UseCounter for, then we should do that.  Assuming the count is very low, then yeah it's probably a trivial removal.

The following revision refers to this bug:
  https://chromium.googlesource.com/chromium/src.git/+/852f5c1f1fd4bcbbe84144e9c9ca69f169be3e63

commit 852f5c1f1fd4bcbbe84144e9c9ca69f169be3e63
Author: jochen <jochen@chromium.org>
Date: Mon Mar 20 17:41:31 2017

Add counters for non-standard background presentation attributes on table

R=rbyers@chromium.org
BUG=703053

Review-Url: https://codereview.chromium.org/2763663002
Cr-Commit-Position: refs/heads/master@{#458112}

[modify] https://crrev.com/852f5c1f1fd4bcbbe84144e9c9ca69f169be3e63/third_party/WebKit/Source/core/frame/UseCounter.h
[modify] https://crrev.com/852f5c1f1fd4bcbbe84144e9c9ca69f169be3e63/third_party/WebKit/Source/core/html/HTMLTableElement.cpp
[modify] https://crrev.com/852f5c1f1fd4bcbbe84144e9c9ca69f169be3e63/third_party/WebKit/Source/core/html/HTMLTablePartElement.cpp
[modify] https://crrev.com/852f5c1f1fd4bcbbe84144e9c9ca69f169be3e63/tools/metrics/histograms/histograms.xml

This issue has been Available for over a year. If it's no longer important or seems unlikely to be fixed, please consider closing it out. If it is important, please re-triage the issue.

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https://www.chromestatus.com/metrics/feature/timeline/popularity/1869

Looks the counter is not ignorable.

So should it rather be added to the HTML spec then?

I created an ad-hoc test in https://software.hixie.ch/utilities/js/live-dom-viewer/saved/5974.

In Chrome, Edge, Firefox and Safari, the background image is shown.

And, as it turns out, this is actually in the spec:
https://html.spec.whatwg.org/multipage/rendering.html#tables-2:attr-background

It doesn't look as though there are any tests for this. Since it's already working the same in all browsers that's very low priority, but filed https://github.com/web-platform-tests/wpt/issues/11235

jochen@, do you want to remove the usecounters again and WontFix this?