Use the new approach, which is simpler and doesn't require to go to the network process to load custom protocols.
Created attachment 379905 [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 http://trac.webkit.org/wiki/WebKitGTK/AddingNewWebKit2API
Oops, I removed the wrong file :-P
Created attachment 379908 [details] Patch
Created attachment 379909 [details] Fix WPE
The linking errors fixed here just by doing a clean build.
Committed r250597: <https://trac.webkit.org/changeset/250597>