Tracking bug for the IndexedDB part of the Content Modularization Project.

https://docs.google.com/document/d/18wpuaitdvki6mO4aWkjvORgryUHM-mvDIqppDXhbSTk/edit# has a high level overview for a possible design.

We should be able to run the IndexedDB database code inside a renderer process. This gives security and stability benefits.

Some task items:
-switch to using quota/blob/leveldb through their new mojo interface, which is required if the IDB code per origin runs in a different process
-new code to handle coordination since IDB would run in multiple renderers
-figuring out what happens if a renderer hosting IDB for an origin crashes, while it's being used by another renderer

The code which stays in the browser process today should be factored out to components/indexeddb. It should avoid dependencies on other parts of content, which is going away per parent bug. This would make it easier to move this code to a profile process once we have one, for further security improvements.