Fix system notifications incorrectly marked as type WEB_PAGE
Some system components were incorrectly calling the Notification
constructor that was intended only for Web Notifications (though this
wasn't clearly documented). I've fixed the incorrect calls, and removed
the confusing constructor to prevent this reoccuring.
Other system components were explicitly constructing a NotifierId using
the constructor that takes a single GURL. I've fixed these incorrect
calls.
Finally, now that Web Notifications can be reliably detected using
`notification->notifier_id().type == NotifierId::WEB_PAGE` I've removed
the obsolete is_web_notification flag from message_center::Notification.
BUG=542232
Review URL: https://codereview.chromium.org/1395093002
Cr-Commit-Position: refs/heads/master@{#353529}
14 files changed
