proxy: consolidate ServicesHandler/EndpointsHandler into ProxyProvider

Proxies should be able to cleanly figure out when endpoints have been synced,
so make all ProxyProviders also implement EndpointsHandler and pass those
through to loadbalancers when required.

pkg/proxy/winuserspace/loadbalancer.go

@@ -19,6 +19,7 @@ package winuserspace
 import (
 	"k8s.io/api/core/v1"
 	"k8s.io/kubernetes/pkg/proxy"
+	proxyconfig "k8s.io/kubernetes/pkg/proxy/config"
 	"net"
 )
 
@@ -30,4 +31,6 @@ type LoadBalancer interface {
 	NewService(service proxy.ServicePortName, sessionAffinityType v1.ServiceAffinity, stickyMaxAgeMinutes int) error
 	DeleteService(service proxy.ServicePortName)
 	CleanupStaleStickySessions(service proxy.ServicePortName)
+
+	proxyconfig.EndpointsHandler
 }