Make HTTP middleware easier to use

common/prpc/talk/helloworld/frontend/prpc.go

 // Copyright 2016 The LUCI Authors. All rights reserved.
 // Use of this source code is governed under the Apache License, Version 2.0
 // that can be found in the LICENSE file.
 
 package helloworld
 
 import (
-        "github.com/julienschmidt/httprouter"
-
         "github.com/luci/luci-go/server/discovery"
-        "github.com/luci/luci-go/server/middleware"
         "github.com/luci/luci-go/server/prpc"
+        "github.com/luci/luci-go/server/router"
 
         "github.com/luci/luci-go/common/prpc/talk/helloworld/proto"
 )
 
-func InstallAPIRoutes(router *httprouter.Router, base middleware.Base) {
+func InstallAPIRoutes(r *router.Router, base router.MiddlewareChain) {
         server := &prpc.Server{}
         helloworld.RegisterGreeterServer(server, &greeterService{})
         discovery.Enable(server)
-        server.InstallHandlers(router, base)
+        server.InstallHandlers(r, base)
 }