We can turn on this feature without actually implementing support for the date picker. This will enable the interior shadow DOM of these input elements allowing for proper input via the keyboard of dates and times. The reasoning for not implementing the date picker UI is that the code currently assumes that the date picker UI can be used without taking focus from the browser window. This isn't as straight-forward to implement in GTK.
Created attachment 426805 [details] Patch
Created attachment 426806 [details] Patch
Thanks for the patch. If this patch contains new public API please make sure it follows the guidelines for new WebKit2 GTK+ API. See https://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Committed r276448 (236908@main): <https://commits.webkit.org/236908@main> All reviewed patches have been landed. Closing bug and clearing flags on attachment 426806 [details].