Initial skeleton of custom layouts for Web Notifications.
This skeleton rendering does the following:
* Render the contents of title, body, origin, time, icon, and icon overlay
* Handles the compact form of the notification
* Uses different styles for v17 (Jelly Bean) and v21 (Material)
It explicitly does not:
* Set padding or positioning or really any exact style quite correctly
* Handle the expanded form or do anything special for the private form
BUG=
541617
Committed:
https://crrev.com/4d99f1d9235c49f77d31e6029dd1c5312836e661
Cr-Commit-Position: refs/heads/master@{#354759}