34236 WARNING: Failed to get localized string for: DOMAttrModifiedEventWarning: file dom/base/nsContentUtils.cpp, line 3769

This warning [1] shows up in the following test suites:

 10310 - test-linux64/debug-jsreftest-e10s-3 J3
 10310 - test-linux64/debug-jsreftest-e10s-1 J1
 10309 - test-linux64/debug-jsreftest-e10s-2 J2
   638 - test-linux64/debug-reftest-e10s-5 R5
   482 - test-linux64/debug-reftest-e10s-1 R1
   467 - test-linux64/debug-reftest-e10s-3 R3
   466 - test-linux64/debug-reftest-e10s-4 R4
   387 - test-linux64/debug-reftest-e10s-6 R6
   353 - test-linux64/debug-reftest-e10s-7 R7
   331 - test-linux64/debug-reftest-e10s-8 R8
   137 - test-linux64/debug-reftest-e10s-2 R2
     9 - test-linux64/debug-mochitest-e10s-2 2
     9 - test-linux64/debug-mochitest-plain-headless-e10s-2 h2
     6 - test-linux64/debug-mochitest-e10s-8 8
     6 - test-linux64/debug-mochitest-plain-headless-e10s-8 h8
     4 - test-linux64/debug-mochitest-chrome-3 c3
     2 - test-linux64/debug-mochitest-e10s-14 14
     2 - test-linux64/debug-mochitest-chrome-1 c1
     1 - test-linux64/debug-mochitest-e10s-4 4
     1 - test-linux64/debug-mochitest-clipboard-e10s cl
     1 - test-linux64/debug-mochitest-browser-chrome-e10s-4 bc4
     1 - test-linux64/debug-mochitest-plain-headless-e10s-4 h4
     1 - test-linux64/debug-mochitest-plain-headless-e10s-15 h15
     1 - test-linux64/debug-mochitest-e10s-5 5
     1 - test-linux64/debug-mochitest-plain-headless-e10s-14 h14
     1 - test-linux64/debug-mochitest-plain-headless-e10s-5 h5

It shows up in 33871 tests. A few of the most prevalent:

     6 - [e10s] about:blank
     4 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/reftest-sanity/scripttest-pass.html
     4 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/image/test/reftest/downscaling/downscale-png.html?16,16,interlaced == file:///builds/worker/workspace/build/tests/reftest/tests/image/test/reftest/downscaling/downscale-png.html?16,16,normal
     4 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/invalidation/filter-userspace-offset.svg?offsetContainer=NNNNNN&filter=NNNNNN-boundingBox == file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/invalidation/filter-userspace-offset.svg
     4 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/image/test/reftest/downscaling/downscale-png.html?24,24,interlaced == file:///builds/worker/workspace/build/tests/reftest/tests/image/test/reftest/downscaling/downscale-png.html?24,24,normal
     3 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/invalidation/filter-userspace-offset.svg?offsetContainer=NNNNNN == file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/invalidation/filter-userspace-offset.svg
     2 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/text-overflow/bidi-simple-scrolled.html == file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/text-overflow/bidi-simple-scrolled-ref.html
     2 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/bidi/dirAuto/1169267-delete-add-1a.html == file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/bidi/dirAuto/1169267-delete-add-1-ref.html
     2 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/dom/html/reftests/596455-1a.html == file:///builds/worker/workspace/build/tests/reftest/tests/dom/html/reftests/596455-ref-1.html
     2 - [e10s] file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/scrolling/fractional-scroll-area.html?top=-0.4&outerBottom=NNNNNN&innerBottom=NNNNNN == file:///builds/worker/workspace/build/tests/reftest/tests/layout/reftests/scrolling/fractional-scroll-area.html?top=NNNNNN&outerBottom=NNNNNN&innerBottom=NNNNNN

[1] https://hg.mozilla.org/try/annotate/4aa6b63a6596/dom/base/nsContentUtils.cpp#l3769

We end up with a ton of debug warnings because we can't localize a web console warning about using the DOMAttrModifiedEvent. This is primarily during jsreftests. I instrumented a build to get a better warning out of nsContentUtils::ReportToConsole, hence the links to a try build above.

There's probably a couple of fixes here:

1. I guess we need a localization entry for this warning?
2. We should probably stop doing whatever it's upset about during jsreftest testing
3. There are a few spots in our codebase that seem to generate this event, I'm not sure if we should be doing that if it's deprecated

Xidorn, it looks like you added the deprecation warning in bug 1461696. I think it's warning because we didn't include a localization line in dom.properties so now we get a warning every time it's called.

As the bug summary indicates, the deprecation warning was added purely for having telemetry for this feature, which was probably for tracking whether bug 1460295 or something alike is serious enough that we should fix.

I don't think we have warning at that time when localization line is not availabe, so I didn't add that.

So, it is safe to remove the related code now, as it is just part of an already-deprecated feature.

https://treeherder.mozilla.org/#/jobs?repo=try&revision=01546cb12ff948556278cea57c8e2769b903674f

It was added in bug 1461696 probably for tracking whether bug 1460295
is a wide-spread issue or so. This deprecation was already part of
deprecated mutation event, so it's never output to console. It was
added purely for getting telemetry.

Given that related issues are now fixed, we no longer needs this.

https://hg.mozilla.org/mozilla-central/rev/904d06bacb8f