48029a897d
Extend the Expect method of a Watcher to allow filter functions that report only an error value, and which "pass" when the reported error is nil. Updates #15160 Change-Id: I582d804554bd1066a9e499c1f3992d068c9e8148 Signed-off-by: M. J. Fromberger <fromberger@tailscale.com>