GitLab

This is a cleanup after:
https://codereview.chromium.org/12794003/

One test for backend force retry is enough, the other test
(CreateBackend_MissingFile) is converted to be backend implementation specific.

The CreateCacheViaPublicInterface() is called only once, but to eliminate it
there is a need to make the cache_thread_ protected. Also, I am sure the name is
not ideal, please suggest another.

The New Eviction allows not to be very strict about version comparison as stored
in the files on disk, this allows creating the BackendImpl with no flags and
then being able to pass the common integrity check.

BUG=173384


Review URL: https://chromiumcodereview.appspot.com/13517004

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@192558 0039d316-1c4b-4281-b951-d872f2087c98