Add NotifyOnShowSettings implementation of notification
provider API and test.

When an extension/app with notificationProvider permission
shows a user that certain notifiers have advanced settings.
When the user clicks and chooses to see advanced settings of
one notifier, NotifyOnShowSettings can be used to inform the
notifier that a user requested advanced settings, so the
notifier can do something else to display its advanced
settings.

BUG=397197

Review URL: https://codereview.chromium.org/456223002

Cr-Commit-Position: refs/heads/master@{#289823}
git-svn-id: svn://svn.chromium.org/chrome/trunk/src@289823 0039d316-1c4b-4281-b951-d872f2087c98
3 files changed