An 'load' event should be fired on the <img> element directly, not an inner element of shadow dom subtree of <img> element which has an author shadow root, when the image is loaded.
Created attachment 158545 [details] load on a shadow host
Comment on attachment 158545 [details] load on a shadow host Clearing flags on attachment: 158545 Committed r125727: <http://trac.webkit.org/changeset/125727>
All reviewed patches have been landed. Closing bug.