Make EntityView use EntityRevision

This replaces the use of EntityContent with EntityRevision in EntityView.
The concrete reason is test state leaking via the database when using
EntityContent, but this change seems to be a good idea in any case.

NOTE: this is incomplete in that it does not remove all uses
of EntityContent from EntityView. This will be done in a follow-up.

Change-Id: I760ef1eb6866698c9050526b19f1653893787402
Remove use of EntityContent from EntityView.

This cleans up EntityView and related classes, removing
references to global state and unneccessary dependencies.

Change-Id: I430dc1f2bde36ee3f8c94ef846a54ebd80fc21f2
Merge changes I430dc1f2,I760ef1eb

* changes:
  Remove use of EntityContent from EntityView.
  Make EntityView use EntityRevision