Remove OnOptInChanged callback.

chrome/browser/chromeos/arc/arc_auth_service.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_AUTH_SERVICE_H_
 #define CHROME_BROWSER_CHROMEOS_ARC_ARC_AUTH_SERVICE_H_
 
 #include <memory>
 #include <ostream>
 #include <string>
@@ skipping 59 matching lines @@
     LSO,                  // LSO page to enter user's credentials.
     START_PROGRESS,       // Arc starting progress page.
     ERROR,                // Arc start error page.
     ERROR_WITH_FEEDBACK,  // Arc start error page, plus feedback button.
   };
 
   class Observer {
    public:
     virtual ~Observer() = default;
 
-    // Called whenever Opt-In state of the ARC has been changed.
-    virtual void OnOptInChanged(State state) {}
-
     // Called to notify that ARC bridge is shut down.
     virtual void OnShutdownBridge() {}
 
     // Called to notify that ARC enabled state has been updated.
     virtual void OnOptInEnabled(bool enabled) {}
 
     // Called to notify that ARC has been initialized successfully.
     virtual void OnInitialStart() {}
   };
 
@@ skipping 171 matching lines @@
 
   DISALLOW_COPY_AND_ASSIGN(ArcAuthService);
 };
 
 // Outputs the stringified |state| to |os|. This is only for logging purposes.
 std::ostream& operator<<(std::ostream& os, const ArcAuthService::State& state);
 
 }  // namespace arc
 
 #endif  // CHROME_BROWSER_CHROMEOS_ARC_ARC_AUTH_SERVICE_H_