Linux native notifications: Require 'actions' and 'body' capabilities

Actions and body text are necessary and expected to be available for
web notifications, so blacklist servers that don't support them.  The
conditions for using native notifications are described at the end of
[1] (Google-only).

[1] https://docs.google.com/a/google.com/document/d/1cqXPpIyCf1RaEYx9XCPjZbO6U5oDeyslajznnG9wd_U/edit?usp=sharing

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

Review-Url: https://codereview.chromium.org/2886903005
Cr-Commit-Position: refs/heads/master@{#472959}
2 files changed