Revert "Remove dead exists method from AccountManager"

This reverts commit 4ae1b67220881a65fe290aa055ae9e085ad95d9e.

We actually wanted to use this method in OpenIdServiceImpl,
but a typo (or bad completion) caused us to use .equals()
instead of .exists() there.

Change-Id: I4811f5c441aaf95b3d85acbb2eb7f1d122a412db
Signed-off-by: Shawn O. Pearce <sop@google.com>
2 files changed