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=.).
$ ls
webkitgtk-3.0.deps webkitgtk-3.0.vapi webkit-sample.vala
$ valac --vapidir=. --pkg gtk+-3.0 --pkg webkitgtk-3.0 --thread webkit-sample.vala
/tmp/fenryxo/webkit-sample.vala.c: In function ‘vala_browser_create_widgets’:
/tmp/fenryxo/webkit-sample.vala.c:206:2: warning: ‘gtk_vbox_new’ is deprecated (declared at /usr/include/gtk-3.0/gtk/deprecated/gtkvbox.h:60): Use 'gtk_box_new' instead [-Wdeprecated-declarations]
$ ls
webkitgtk-3.0.deps webkitgtk-3.0.vapi webkit-sample webkit-sample.vala