Change userid from a uint32_t to a string guid

mojo/shell/background/background_shell.cc

 // Copyright 2016 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.
 
 #include "mojo/shell/background/background_shell.h"
 
 #include "base/bind.h"
 #include "base/bind_helpers.h"
 #include "base/command_line.h"
 #include "base/logging.h"
@@ skipping 160 matching lines @@
 
 void BackgroundShell::Init(scoped_ptr<InitParams> init_params) {
   DCHECK(!thread_);
   thread_.reset(new MojoThread(std::move(init_params)));
   thread_->Start();
 }
 
 mojom::ShellClientRequest BackgroundShell::CreateShellClientRequest(
     const std::string& name) {
   scoped_ptr<ConnectParams> params(new ConnectParams);
-  params->set_target(Identity(name, std::string(),
-                              mojom::Connector::kUserRoot));
+  params->set_target(Identity(name, std::string(), mojom::kRootUserID));
   mojom::ShellClientRequest request;
   base::WaitableEvent signal(true, false);
   thread_->message_loop()->task_runner()->PostTask(
       FROM_HERE, base::Bind(&MojoThread::CreateShellClientRequest,
                             base::Unretained(thread_.get()), &signal,
                             base::Passed(&params), &request));
   signal.Wait();
   return request;
 }
 
 }  // namespace shell
 }  // namespace mojo