Change userid from a uint32_t to a string guid

mojo/services/network/network_service_delegate.h

Index: mojo/services/network/network_service_delegate.h
diff --git a/mojo/services/network/network_service_delegate.h b/mojo/services/network/network_service_delegate.h
index 0c444adf1b41416129e2bb48fbfbae2a1e51ddc3..07e93b5aecb8c8825fdda2ac78ef109fa3a8406c 100644
--- a/mojo/services/network/network_service_delegate.h
+++ b/mojo/services/network/network_service_delegate.h
@@ -36,7 +36,7 @@ class NetworkServiceDelegate : public ShellClient,
  private:
   // mojo::ShellClient implementation.
   void Initialize(Connector* connector, const std::string& url,
-                  uint32_t id, uint32_t user_id) override;
+                  const std::string& user_id, uint32_t id) override;
   bool AcceptConnection(Connection* connection) override;
 
   // InterfaceFactory<NetworkService> implementation.