The recently-added assertion in Node::setDocument(), willMoveToNewOwnerDocumentWasCalled, fails when adopting a <form> element. To reproduce, open the attached test case.
Created attachment 30159 [details] Test case (will ASSERT)
Created attachment 30160 [details] Make HTMLFormElement call the base class implementation of {will,did}MoveToNewOwnerDocument
Comment on attachment 30160 [details] Make HTMLFormElement call the base class implementation of {will,did}MoveToNewOwnerDocument r=me
Fixed in <http://trac.webkit.org/projects/webkit/changeset/43451>.