Linux native notifications:  Handle clicks and closes

This CL adds the initial wiring to GLib and
NativeNotificationDisplayService to get actions and closes working.

BUG=676220
R=thestig@chromium.org,peter@chromium.org

Review-Url: https://codereview.chromium.org/2805543005
Cr-Commit-Position: refs/heads/master@{#463045}
2 files changed