Simplify permission-related code for Web Notifications.
(1) Remove support for inheriting the "notification" API permission
for packaged and hosted apps using the Web Notification API. This
has been inadvertently broken since Chrome 42.
(2) Give notifications a dedicated NotificationPermissionContext,
similar to those other features have. (+ unit tests)
(3) Remove and clean up all unused code.
This further emphasizes the DesktopNotificationService as a deprecated
concept. I'll remove it entirely in a follow-up patch.
BUG=504361
Review URL: https://codereview.chromium.org/
1207363002
Cr-Commit-Position: refs/heads/master@{#337206}