Display off is done by a callback into backlight controller

backlight_controller.h

 // Copyright (c) 2011 The Chromium OS 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 POWER_MANAGER_BACKLIGHT_CONTROLLER_H_
 #define POWER_MANAGER_BACKLIGHT_CONTROLLER_H_
 
 #include <algorithm>
 
 #include "power_manager/backlight_interface.h"
@@ skipping 80 matching lines @@
   // by other programs to our local view. Return true if the brightness
   // has not been modified by other programs; return false otherwise.
   bool ReadBrightness();
 
   // Write brightness based on current settings.
   // Returns true if the brightness was changed and false otherwise.
   bool WriteBrightness();
 
   void SetBrightnessToZero();
 
-  // Turn off the display if the backlight has been turned off.
-  SIGNAL_CALLBACK_0(BacklightController, gboolean, DisplayOffWhenBacklightOff);
+  // Indicates whether the display should be turned off based on the current
+  // power state.
+  SIGNAL_CALLBACK_0(BacklightController, void, TurnScreenOff);
 
   // Backlight used for dimming. Non-owned.
   BacklightInterface* backlight_;
 
   // Interface for saving preferences. Non-owned.
   PowerPrefsInterface* prefs_;
 
   // Light sensor we need to enable/disable on power events.  Non-owned.
   AmbientLightSensor* light_sensor_;
 
@@ skipping 28 matching lines @@
 
   // Flag is set if a backlight device exists.
   bool is_initialized_;
 
   DISALLOW_COPY_AND_ASSIGN(BacklightController);
 };
 
 }  // namespace power_manager
 
 #endif  // POWER_MANAGER_BACKLIGHT_CONTROLLER_H_