health, all: remove health.Global, finish plumbing health.Tracker

Updates #11874
Updates #4136

Change-Id: I414470f71d90be9889d44c3afd53956d9f26cd61
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

control/controlhttp/client.go

@@ -38,7 +38,6 @@ import (
 
 	"tailscale.com/control/controlbase"
 	"tailscale.com/envknob"
-	"tailscale.com/health"
 	"tailscale.com/net/dnscache"
 	"tailscale.com/net/dnsfallback"
 	"tailscale.com/net/netutil"
@@ -434,7 +433,7 @@ func (a *Dialer) tryURLUpgrade(ctx context.Context, u *url.URL, addr netip.Addr,
 	// Disable HTTP2, since h2 can't do protocol switching.
 	tr.TLSClientConfig.NextProtos = []string{}
 	tr.TLSNextProto = map[string]func(string, *tls.Conn) http.RoundTripper{}
-	tr.TLSClientConfig = tlsdial.Config(a.Hostname, health.Global, tr.TLSClientConfig)
+	tr.TLSClientConfig = tlsdial.Config(a.Hostname, a.HealthTracker, tr.TLSClientConfig)
 	if !tr.TLSClientConfig.InsecureSkipVerify {
 		panic("unexpected") // should be set by tlsdial.Config
 	}

control/controlhttp/constants.go

@@ -8,6 +8,7 @@ import (
 	"net/url"
 	"time"
 
+	"tailscale.com/health"
 	"tailscale.com/net/dnscache"
 	"tailscale.com/net/netmon"
 	"tailscale.com/tailcfg"
@@ -79,6 +80,9 @@ type Dialer struct {
 
 	NetMon *netmon.Monitor
 
+	// HealthTracker, if non-nil, is the health tracker to use.
+	HealthTracker *health.Tracker
+
 	// DialPlan, if set, contains instructions from the control server on
 	// how to connect to it. If present, we will try the methods in this
 	// plan before falling back to DNS.