Do not send out SIGNIN_SUCCESSFUL notifications with empty passphrases.
Do not send out SIGNIN_SUCCESSFUL notifications with empty passphrases.

Fixes case in cros where a restart after a browser crash would pass along
an empty passphrase to ProfileSyncService.

BUG=121159
TEST=Restart after browser crash

Review URL: https://chromiumcodereview.appspot.com/9968023

git-svn-id: de016e52bd170d2d4f2344f9bf92d50478b649e0@130440 0039d316-1c4b-4281-b951-d872f2087c98

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