Change userid from a uint32_t to a string guid

mash/screenlock/screenlock.h

 // 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.
 
 #ifndef MASH_SCREENLOCK_SCREENLOCK_H_
 #define MASH_SCREENLOCK_SCREENLOCK_H_
 
 #include <map>
 
 #include "base/macros.h"
@@ skipping 12 matching lines @@
 
 class Screenlock : public mojo::ShellClient,
                    public shell::mojom::ScreenlockStateListener {
  public:
   Screenlock();
   ~Screenlock() override;
 
  private:
   // mojo::ShellClient:
   void Initialize(mojo::Connector* connector, const std::string& url,
-                  uint32_t id, uint32_t user_id) override;
+                  const std::string& user_id, uint32_t id) override;
 
   // mash::shell::mojom::ScreenlockStateListener:
   void ScreenlockStateChanged(bool locked) override;
 
   mojo::TracingImpl tracing_;
   scoped_ptr<views::AuraInit> aura_init_;
   mojo::BindingSet<mash::shell::mojom::ScreenlockStateListener> bindings_;
 
   DISALLOW_COPY_AND_ASSIGN(Screenlock);
 };
 
 }  // namespace screenlock
 }  // namespace mash
 
 #endif  // MASH_SCREENLOCK_SCREENLOCK_H_