* In this CL, we cache individual rows, based on the CONTENT_PROJECTION
defined for the most common queries (Account, HostAuth, Mailbox, and
Message)
* Queries on individual rows (most often Class.restoreClassById()) will
look to the cache first, rather than querying the database
* Queries on smaller projections will build MatrixCursor's from cached
data
* Write-through caching updates the cache with changed columns
* Experiments with live data indicate that > 95% of queries that are
cacheable (single row, no selection) can be retrieved from the cache,
thereby saving a great deal of disk access.
* Timing experiments show that cache hits are > 40x faster than cache
misses
* Unit tests for the various classes exist, with more coming
TODO
----
* More unit tests
Change-Id: I386a948a2f4cc02b6548d07d9b2fefd1e018a262
fab77f147f