LogDog: Add prefix registration endpoint.

common/api/logdog_coordinator/registration/v1/registrationserver_dec.go

 // Code generated by svcdec; DO NOT EDIT
 
 package logdog
 
 import (
         proto "github.com/golang/protobuf/proto"
         context "golang.org/x/net/context"
-
-        google_protobuf "github.com/luci/luci-go/common/proto/google"
 )
 
-type DecoratedAdmin struct {
+type DecoratedRegistration struct {
         // Service is the service to decorate.
-        Service AdminServer
+        Service RegistrationServer
         // Prelude is called in each method before forwarding the call to Service.
         // If Prelude returns an error, it is returned without forwarding the call.
         Prelude func(c context.Context, methodName string, req proto.Message) (context.Context, error)
 }
 
-func (s *DecoratedAdmin) SetConfig(c context.Context, req *SetConfigRequest) (*google_protobuf.Empty, error) {
-        c, err := s.Prelude(c, "SetConfig", req)
+func (s *DecoratedRegistration) RegisterPrefix(c context.Context, req *RegisterPrefixRequest) (*RegisterPrefixResponse, error) {
+        c, err := s.Prelude(c, "RegisterPrefix", req)
         if err != nil {
                 return nil, err
         }
-        return s.Service.SetConfig(c, req)
+        return s.Service.RegisterPrefix(c, req)
 }