Change userid from a uint32_t to a string guid

mojo/shell/public/interfaces/shell.mojom

 // Copyright 2015 The Chromium Authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 module mojo.shell.mojom;
 
 import "mojo/shell/public/interfaces/connector.mojom";
 import "mojo/shell/public/interfaces/shell_client_factory.mojom";
 
 struct InstanceInfo {
@@ skipping 48 matching lines @@
 };
 
 interface Shell {
   // Instructs the Shell to create an instance for an existing process at the
   // other end of |factory|, and perform applicable initialization. |user_id| is
   // the user the instance should be created as. This is typically set to
   // Connector::kUserInherit, unless the application has the ability to connect
   // as other users.
   CreateInstanceForFactory(ShellClientFactory factory,
                            string name,
-                           uint32 user_id,
+                           string user_id,
                            CapabilityFilter filter,
                            PIDReceiver& pid_receiver);
 
   // The listener is removed when the |listener| pipe is closed.
   AddInstanceListener(InstanceListener listener);
 };