Make HTTP middleware easier to use

appengine/gaemiddleware/context.go

Index: appengine/gaemiddleware/context.go
diff --git a/appengine/gaemiddleware/context.go b/appengine/gaemiddleware/context.go
index 60a8bce83791c2a309cd777a9bd2c7ade7e19373..b8da7cc1e39949972f6a8e418ddfb5ba121d76d2 100644
--- a/appengine/gaemiddleware/context.go
+++ b/appengine/gaemiddleware/context.go
@@ -9,7 +9,6 @@ import (
 
 	"google.golang.org/appengine"
 
-	"github.com/julienschmidt/httprouter"
 	"golang.org/x/net/context"
 
 	"github.com/luci/gae/filter/dscache"
@@ -25,6 +24,7 @@ import (
 	"github.com/luci/luci-go/server/auth"
 	"github.com/luci/luci-go/server/middleware"
 	"github.com/luci/luci-go/server/proccache"
+	"github.com/luci/luci-go/server/router"
 	"github.com/luci/luci-go/server/settings"
 )
 
@@ -78,12 +78,14 @@ func WithProd(c context.Context, req *http.Request) context.Context {
 //
 // It installs services using WithProd, installs a panic catcher if this
 // is not a devserver, and injects the monitoring middleware.
-func BaseProd(h middleware.Handler) httprouter.Handle {
-	h = globalTsMonState.Middleware(h)
+func BaseProd() []router.Handler {
+	var h []router.Handler
+	h = append(h, func(c *router.Context) {
+		c.Context = WithProd(context.Background(), c.Request)
+	})
 	if !appengine.IsDevAppServer() {
-		h = middleware.WithPanicCatcher(h)
-	}
-	return func(rw http.ResponseWriter, r *http.Request, p httprouter.Params) {
-		h(WithProd(context.Background(), r), rw, r, p)
+		h = append(h, middleware.WithPanicCatcher())
 	}
+	h = append(h, globalTsMonState.Middleware())
+	return h
 }