arc: Implement safe access to ArcAuthService.

chrome/browser/chromeos/arc/arc_support_host.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 CHROME_BROWSER_CHROMEOS_ARC_ARC_SUPPORT_HOST_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_ARC_SUPPORT_HOST_H_
 
 #include "base/macros.h"
 #include "chrome/browser/chromeos/arc/arc_auth_service.h"
 #include "components/prefs/pref_change_registrar.h"
@@ skipping 26 matching lines @@
 
   // display::DisplayObserver:
   void OnDisplayAdded(const display::Display& new_display) override;
   void OnDisplayRemoved(const display::Display& old_display) override;
   void OnDisplayMetricsChanged(const display::Display& display,
                                uint32_t changed_metrics) override;
 
  private:
   ArcSupportHost();
 
+  bool Initialize();
   void OnMetricsPreferenceChanged();
-  void Initialize();
   void SendMetricsMode();
   void EnableMetrics(bool is_enabled);
   void EnableBackupRestore(bool is_enabled);
 
   // Unowned pointer.
   Client* client_ = nullptr;
 
   // Used to track metrics preference.
   PrefChangeRegistrar pref_change_registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(ArcSupportHost);
 };
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_SUPPORT_HOST_H_