When running tests in WebKitTestRunner, after running LayoutTests/fast/css/user-drag-none.html its document is kept alive by DragController as m_documentUnderMouse. For some reason, DragController never gets dragExited() or dragEnded() in WebKitTestRunner, but it does in DumpeRenderTree.
<rdar://problem/40756588>
<rdar://problem/40756694>