A few highlights
- Always use one kind of profile id (the stable one)
- Always use a single notification id (the persistent one when possible)
- The mac implementation injects the NSUSerNotificationService to allow unittests

Note that the mac and android files are not renamed. Ideally I would land this and then land a straight forward rename cl.

BUG=571056,596161

Review URL: https://codereview.chromium.org/1814923002

Cr-Commit-Position: refs/heads/master@{#388776}