Write design doc for how Web Manifest short_name and name will be stored in the database

The design doc should outline:
- which new classes are required
- what database changes are necessary
- who stores the name and short_name into the database (FaviconHandler? something else?)

I think the three options that we have are:
- Store the short_name and name somewhere in the favicon database (likely a new table)
- Create a new database whose role is to store Web Manifests. This would still be accessed via the HistoryService
- Store this information in the top sites database using something similar to ThumbnailTabHelper

My initial preference is for the top sites solution. The new information is useful for just the NTP and top-sites is NTP specific. I don't know whether this solution involves more code than the other solutions