Make SetDisplayPower() take a callback to signal completion

chrome/browser/chromeos/dbus/chrome_display_power_service_provider_delegate.cc

 // 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.
 
 #include "chrome/browser/chromeos/dbus/chrome_display_power_service_provider_delegate.h"
 
 #include "ash/shell.h"
 #include "ui/base/user_activity/user_activity_detector.h"
 #include "ui/display/chromeos/display_configurator.h"
 
 namespace chromeos {
 
 ChromeDisplayPowerServiceProviderDelegate::
 ChromeDisplayPowerServiceProviderDelegate() {
 }
 
 ChromeDisplayPowerServiceProviderDelegate::
 ~ChromeDisplayPowerServiceProviderDelegate() {
 }
 
 void ChromeDisplayPowerServiceProviderDelegate::SetDisplayPower(
-    DisplayPowerState power_state) {
+    DisplayPowerState power_state,
+    const ResponseCallback& callback) {
   // Turning displays off when the device becomes idle or on just before
   // we suspend may trigger a mouse move, which would then be incorrectly
   // reported as user activity.  Let the UserActivityDetector
   // know so that it can ignore such events.
   ui::UserActivityDetector::Get()->OnDisplayPowerChanging();
 
   ash::Shell::GetInstance()->display_configurator()->SetDisplayPower(
-      power_state, ui::DisplayConfigurator::kSetDisplayPowerNoFlags);
+      power_state, ui::DisplayConfigurator::kSetDisplayPowerNoFlags, callback);
 }
 
 void ChromeDisplayPowerServiceProviderDelegate::SetDimming(bool dimmed) {
   ash::Shell::GetInstance()->SetDimming(dimmed);
 }
 
 }  // namespace chromeos