Make HTTP middleware easier to use

appengine/tsmon/middleware.go

Index: appengine/tsmon/middleware.go
diff --git a/appengine/tsmon/middleware.go b/appengine/tsmon/middleware.go
index 5014b81405ede68ee3d3871daf5ac36050a29b28..5957d6ba1fea77557d7c87303eb2aee53d1b4ec3 100644
--- a/appengine/tsmon/middleware.go
+++ b/appengine/tsmon/middleware.go
@@ -10,13 +10,11 @@ package tsmon
 
 import (
 	"fmt"
-	"net/http"
 	"strings"
 	"sync"
 	"time"
 
 	"github.com/golang/protobuf/proto"
-	"github.com/julienschmidt/httprouter"
 	"golang.org/x/net/context"
 
 	"github.com/luci/gae/service/info"
@@ -28,7 +26,7 @@ import (
 	"github.com/luci/luci-go/common/tsmon/monitor"
 	"github.com/luci/luci-go/common/tsmon/store"
 	"github.com/luci/luci-go/common/tsmon/target"
-	"github.com/luci/luci-go/server/middleware"
+	"github.com/luci/luci-go/server/router"
 )
 
 // State holds the configuration of the tsmon library for GAE.
@@ -61,12 +59,12 @@ type State struct {
 
 // Middleware returns a middleware that must be inserted into the chain to
 // enable tsmon metrics to be sent on App Engine.
-func (s *State) Middleware(h middleware.Handler) middleware.Handler {
-	return func(c context.Context, rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
-		state, settings := s.checkSettings(c)
-		h(c, rw, r, p)
+func (s *State) Middleware() router.Handler {
+	return func(c *router.Context) {
+		state, settings := s.checkSettings(c.Context)
+		c.Next()
 		if settings.Enabled {
-			s.flushIfNeeded(c, state, settings)
+			s.flushIfNeeded(c.Context, state, settings)
 		}
 	}
 }