Bug 51032

- It uses both glib private data and it allocates its own private structure - It calls parent's dispose method from finalize - webkit_web_plugin_get_mimetypes() uses a wrong annotation for the returned value, it should be transfer none rather than transfer container. - Since the mime type list is internal and we return the list and not a copy, it should never be freed by the caller, so webkit_web_plugin_mime_type_list_free() should be removed from the public API. - Mime types list is used uninitialized - Mention in the docs that list returned by webkit_web_plugin_database_get_plugins() must be freed with webkit_web_plugin_database_plugins_list_free()