chromeos: Remove old LockScreen signal.

chrome/browser/chromeos/power/power_button_observer.h

 // Copyright (c) 2012 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_POWER_POWER_BUTTON_OBSERVER_H_
 #define CHROME_BROWSER_CHROMEOS_POWER_POWER_BUTTON_OBSERVER_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "chromeos/dbus/power_manager_client.h"
@@ skipping 16 matching lines @@
  private:
   // content::NotificationObserver implementation:
   virtual void Observe(int type,
                        const content::NotificationSource& source,
                        const content::NotificationDetails& details) OVERRIDE;
 
   // PowerManagerObserver implementation:
   virtual void PowerButtonEventReceived(
       bool down, const base::TimeTicks& timestamp) OVERRIDE;
 
-  // SessionManagerClient::Observer implementation:
-  // TODO(derat): Remove this once the session manager is making LockScreen
-  // method calls instead.
-  virtual void LockScreen() OVERRIDE;
-
   content::NotificationRegistrar registrar_;
 
   DISALLOW_COPY_AND_ASSIGN(PowerButtonObserver);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_POWER_POWER_BUTTON_OBSERVER_H_