This is an expected keybinding, and it is not hard to support. Note that we use a private ::escape signal instead of using ::cancel directly, since we want to be able to suppress the cancellation when we are on a progress page.
https://bugzilla.gnome.org/show_bug.cgi?id=579625
ffe0ec6 GtkAssistant: Make Escape cancel the assistant
gtk/gtkassistant.c | 29 +++++++++++++++++++++++++++++
1 file changed, 29 insertions(+)
Upstream: git.gnome.org