There are lots of tests running on content-level XUL document which check some XUL functionality. They use backdoors to enable XUL support. Having stylo run on those tests means we would be able to observe the progress on XUL support of Stylo, and avoid any regression on that support. Since those backdoors are only enabled in tests as I investigated in bug 1400540 comment 24, removing the XUL document check in UpdateStyleBackendType isn't expected to break anything in the product. If it does, we should blacklist any offending page in ShouldUseGeckoBackend.

This is an initial try run: https://treeherder.mozilla.org/#/jobs?repo=try&revision=e5179ca6ae3804c6a9fdaf948f1ae863c895d209

Nice one, thanks for doing this Xidorn! :)

So the biggest issues in terms of test are bug 1408235 (affects everything), bug 1397644 (generates tons of assertions), and bug 1408811 (affects almost all tests involve textbox / editor).

Comment on attachment 8918755 [details] Bug 1407847 - Enable stylo for XUL document without system principal and annotate failures accordingly. https://reviewboard.mozilla.org/r/189594/#review194814 ::: layout/reftests/reftest.list:407 (Diff revision 1) > include ../../dom/tests/reftest/xml-stylesheet/reftest.list > > # xul-document-load/ (no XUL theme on Android) > -skip-if(Android) include xul-document-load/reftest.list > +# skip for stylo because the reference page is wrong due to bug 1408235. > +# There are some pages rendered incorrectly in the same way, so this > +# test test set is basically broken and not worth further annotating. One too many "test"s.

Pushed by xquan@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/806b195734ee Enable stylo for XUL document without system principal and annotate failures accordingly. r=heycam

Pushed by xquan@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/a56e238457f4 followup - Annotate more tests.

Pushed by xquan@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/a4feebaedce8 followup 2 - Adjust some assertions annotation.

Pushed by xquan@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/4b553367eb72 followup 3 - Update one asserts-if for styloVsGecko.

Pushed by ecoal95@gmail.com: https://hg.mozilla.org/integration/autoland/rev/9d5720ca5a1b followup: Adjust crashtest assert count expectation. r=me

Pushed by xquan@mozilla.com: https://hg.mozilla.org/integration/autoland/rev/81d815452d89 followup 3 - Adjust some assert count expectation on a CLOSED TREE.

https://hg.mozilla.org/mozilla-central/rev/806b195734ee https://hg.mozilla.org/mozilla-central/rev/a56e238457f4 https://hg.mozilla.org/mozilla-central/rev/a4feebaedce8 https://hg.mozilla.org/mozilla-central/rev/4b553367eb72 https://hg.mozilla.org/mozilla-central/rev/9d5720ca5a1b https://hg.mozilla.org/mozilla-central/rev/81d815452d89