ipc: Add some type checking statements

Change-Id: I20547b932efc89352a33c6307e01fda9590c6db6
diff --git a/runtimes/google/ipc/stream/manager/manager.go b/runtimes/google/ipc/stream/manager/manager.go
index fc5491f..7afdad3 100644
--- a/runtimes/google/ipc/stream/manager/manager.go
+++ b/runtimes/google/ipc/stream/manager/manager.go
@@ -46,6 +46,8 @@
 	shutdown    bool              // GUARDED_BY(muListeners)
 }
 
+var _ stream.Manager = (*manager)(nil)
+
 func dial(network, address string) (net.Conn, error) {
 	if d, _ := stream.RegisteredProtocol(network); d != nil {
 		return d(address)