/usr/share/glib-2.0/schemas/10_epiphany-browser-data.gschema.override is in epiphany-browser-data 3.4.0.1-2ubuntu1.
This file is owned by root:root, with mode 0o644.
The actual contents of the file can be viewed below.
1 2 | [org.gnome.Epiphany]
keyword-search-url='http://www.google.com/search?client=ubuntu&channel=es&q=%s&ie=UTF-8&oe=UTF-8'
|