In the case of GTK port, it allows to use a custom IM instead of GtkIMContext that it's still used by default. In the case of WPE it bring IM support, but there's no default implementation so applications need to provide their own.
Created attachment 384451 [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
Committed r253749: <https://trac.webkit.org/changeset/253749>