The following DRT tests in fast/mutation fail due to lack of WebkitMutationObserver/ENABLE(MUTATION_OBSERVERS):
fast/mutation/cross-document.html
fast/mutation/mutation-observer-constructor.html
fast/mutation/observe-attributes.html
fast/mutation/observe-characterdata.html
fast/mutation/observe-childList.html
fast/mutation/observe-exceptions.html
fast/mutation/observe-subtree.html
fast/mutation/database-callback-delivery.html
fast/mutation/end-of-task-delivery.html
fast/mutation/filesystem-callback-delivery.html
fast/mutation/inline-event-listener.html

I'll exclude these tests as the feature seems to be disabled in our WebKit bild.