Created attachment 255454 [details]
Try to drag and drop anything from the web view with GTK+ 3.17.2 or higher. The UI process will crash with the attached backtrace.
The problem is in WebKit::DragAndDropHandler::startDrag:
GdkDragContext* context = gtk_drag_begin(m_page.viewWidget(), targetList.get(), dragOperationToGdkDragActions(dragData.draggingSourceOperationMask()),
gtk_get_current_event is nullable but the last parameter to gtk_drag_begin is not, so we should check to ensure it is not null here. This of course does not fix drag and drop, but it does fix the crash. Without this, the web process could force the UI process to crash by sending fake startDrag messages.
Created attachment 255455 [details]
Comment on attachment 255455 [details]
Clearing flags on attachment: 255455
Committed r185896: <http://trac.webkit.org/changeset/185896>
All reviewed patches have been landed. Closing bug.
Re-opened since this is blocked by bug 146647