Make SetDisplayPower() take a callback to signal completion

chrome/browser/chromeos/dbus/chrome_display_power_service_provider_delegate.h

 // Copyright 2014 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_DBUS_CHROME_DISPLAY_POWER_SERVICE_PROVIDER_DELEGATE_H_
 #define CHROME_BROWSER_CHROMEOS_DBUS_CHROME_DISPLAY_POWER_SERVICE_PROVIDER_DELEGATE_H_
 
 #include "chromeos/dbus/services/display_power_service_provider.h"
 
 namespace chromeos {
 
 // Chrome's implementation of DisplayPowerServiceProvider::Delegate
 class ChromeDisplayPowerServiceProviderDelegate
     : public DisplayPowerServiceProvider::Delegate {
  public:
   ChromeDisplayPowerServiceProviderDelegate();
   ~ChromeDisplayPowerServiceProviderDelegate() override;
 
   // DisplayPowerServiceProvider::Delegate overrides:
-  void SetDisplayPower(DisplayPowerState power_state) override;
+  void SetDisplayPower(DisplayPowerState power_state,
+                       const ResponseCallback& callback) override;
   void SetDimming(bool dimmed) override;
 
  private:
   DISALLOW_COPY_AND_ASSIGN(ChromeDisplayPowerServiceProviderDelegate);
 };
 
 }  // namespace chromeos
 
 #endif  // CHROME_BROWSER_CHROMEOS_DBUS_CHROME_DISPLAY_POWER_SERVICE_PROVIDER_DELEGATE_H_