wspr: Add addToRoots() for js

MultiPart: 2/2

Change-Id: Id8693636f776b665703c3e83c2314d7bcd213a7b
diff --git a/services/wspr/internal/app/controller.vdl b/services/wspr/internal/app/controller.vdl
index ff4f1c0..85c911a 100644
--- a/services/wspr/internal/app/controller.vdl
+++ b/services/wspr/internal/app/controller.vdl
@@ -32,6 +32,8 @@
 	BlessSelf(name string, caveats []security.Caveat) (string, principal.BlessingsHandle | error)
 	// PutToBlessingStore puts the specified blessing to the blessing store under the provided pattern.
 	PutToBlessingStore(blessingHandle principal.BlessingsHandle, pattern security.BlessingPattern) (?principal.JsBlessings | error)
+	// AddToRoots adds the provided blessing as a root.
+	AddToRoots(blessingHandle principal.BlessingsHandle) error
 
 	// RemoteBlessings fetches the remote blessings for a given name and method.
 	RemoteBlessings(name, method string) ([]string | error)