Define cros event names for chaps database failures.

BUG=chrome-os-partner:17610
TEST=emerge

Change-Id: Ic12379645ad1c72388aa4a4758fa4bea5b2f554d
Reviewed-on: https://gerrit.chromium.org/gerrit/62698


Reviewed-by: Gaurav Shah <gauravsh@chromium.org>
Commit-Queue: Darren Krahn <dkrahn@chromium.org>
Tested-by: Darren Krahn <dkrahn@chromium.org>