Fix schema for AutoCleanUpStrategy policy

The AutoCleanUpStrategy policy can take on one of two values. Both should
be listed in the schema.

BUG=306334
TEST=None

Review URL: https://codereview.chromium.org/136633003

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@244563 0039d316-1c4b-4281-b951-d872f2087c98
SVN changes up to revision 244563