Add the reported testcase to WPT
I don't reproduce the crash even if I rewrite the test using attachShadow
which replaced createShadowRoot. Therefore, this patch just adds the reported
testcase into the tree.
Differential Revision: https://phabricator.services.mozilla.com/D213375
bugzilla-url: https://bugzilla.mozilla.org/show_bug.cgi?id=1414893
gecko-commit: 954e0f01f6b1394c3d71478c703417994a134dcc
gecko-reviewers: sefeng