As the title says my problem is that I try to use both gtk 3 and webkit 1.
I am following this example https://live.gnome.org/Vala/WebKitSample
except that I am using gtk 3 instead of 2.
I am using valac 0.16.0
I have now noticed that errors are Gdk 2 and Gdk 3 same symbols.
This seems like a way to solve my problems link
but it is nonstandard.
Nevermind, I have fixed it with a bundled webkitgtk.
You cannot use library webkit-1.0 with gtk+-3.0, because webkit-1.0 depends on gtk+-2.0 and gdk-2.0 that conflict with gtk+-3.0 and gdk-3.0. You have to use library webkitgtk-3.0 that has same API as webkit-1.0, but depends on gtk+-3.0 and gdk-3.0.
Since webkigtk-3.0 bindings are not shipped with Vala (bug 676249), you have to create your own bindings (follow instructions in the mentioned e-mail) and tell valac where your webkigtk-3.0.vapi file is located (
--vapidir=.).