HTMLTemplateElement should create a signleton owner document
that's shared amongst all of its "inert" contents.
This bug was found by the newly added test:
html/semantics/scripting-1/the-template-element/definitions/template-contents-owner-test-001.html also fails because of this bug.
Oh oops, I uploaded the patch to a wrong bug :(
*** This bug has been marked as a duplicate of bug 154936 ***