In prep for tsd.System Tracker plumbing throughout tailscaled,
defensively permit all methods on Tracker to accept a nil receiver
without crashing, lest I screw something up later. (A health tracking
system that itself causes crashes would be no good.) Methods on nil
receivers should not be called, so a future change will also collect
their stacks (and panic during dev/test), but we should at least not
crash in prod.
This also locks that in with a test using reflect to automatically
call all methods on a nil receiver and check they don't crash.
Updates #11874
Updates #4136
Change-Id: I8e955046ebf370ec8af0c1fb63e5123e6282a9d3
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
Brad FitzpatrickandBrad Fitzpatrick
cb66952a0d