Notification settings for ephemeral apps

Only running ephemeral apps will appear in the notification settings
pane. This avoids spamming the list with inactive cached ephemeral apps.

The setting will also be persisted across cache evictions, so that
notifications will still be disabled when the ephemeral app is
re-cached at a later date.

BUG=343453
TEST=browser_tests (EphemeralAppBrowserTest.StickyNotificationSettings)

Review URL: https://codereview.chromium.org/163953012

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@251754 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 251754