Milo: Use custom config caching layer

milo/appengine/swarming/html.go

Index: milo/appengine/swarming/html.go
diff --git a/milo/appengine/swarming/html.go b/milo/appengine/swarming/html.go
index 4458d232d7214592f5cef66a8a86009933c954e5..6ff09ff7bb1dfc17a437e2e9bcab031509e099e0 100644
--- a/milo/appengine/swarming/html.go
+++ b/milo/appengine/swarming/html.go
@@ -30,13 +30,9 @@ var errUnrecognizedHost = errors.New("Unregistered Swarming Host")
 // none is specified, get the default swarming host out of the global
 // configs.
 func getSwarmingHost(c context.Context, r *http.Request) (string, error) {
-	settings, err := common.GetSettings(c)
-	if err != nil {
-		logging.WithError(err).Errorf(c, "could not get settings")
-		return "", err
-	}
+	settings := common.GetSettings(c)
 	if settings.Swarming == nil {
-		err = errors.New("swarming not in settings")
+		err := errors.New("swarming not in settings")
 		logging.Errorf(c, err.Error())
 		return "", err
 	}