Display off is done by a callback into backlight controller

backlight_controller.cc

 // 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.
 
 #include "power_manager/backlight_controller.h"
 
 #include <gdk/gdkx.h>
 #include <math.h>
 #include <X11/extensions/dpms.h>
 
@@ skipping 49 matching lines @@
       system_brightness_(0),
       min_(0),
       max_(-1),
       is_initialized_(false) {}
 
 bool BacklightController::Init() {
   int64 level;
   if (backlight_->GetBrightness(&level, &max_)) {
     ReadPrefs();
     is_initialized_ = true;
+    backlight_->SetScreenOffFunc(TurnScreenOffThunk, this);
     return true;
   }
   return false;
 }
 
 bool BacklightController::GetBrightness(int64* level) {
   int64 raw_level;
   if (!backlight_->GetBrightness(&raw_level, &max_))
     return false;
   *level = lround(100. * raw_level / max_);
@@ skipping 62 matching lines @@
   if (light_sensor_)
     light_sensor_->EnableOrDisableSensor(state_);
 
   if (GDK_DISPLAY() == NULL)
     return changed_brightness;
   if (!DPMSCapable(GDK_DISPLAY())) {
     LOG(WARNING) << "X Server is not DPMS capable";
   } else {
     CHECK(DPMSEnable(GDK_DISPLAY()));
     if (state == BACKLIGHT_IDLE_OFF) {
-      g_timeout_add(kDisplayOffDelayMS, DisplayOffWhenBacklightOffThunk, this);
       SetBrightnessToZero();
     } else if (state == BACKLIGHT_ACTIVE_ON) {
       CHECK(DPMSForceLevel(GDK_DISPLAY(), DPMSModeOn));
     }
   }
   return changed_brightness;
 }
 
 bool BacklightController::OnPlugEvent(bool is_plugged) {
   if ((brightness_offset_ && is_plugged == plugged_state_) || !is_initialized_)
@@ skipping 129 matching lines @@
 }
 
 void BacklightController::SetBrightnessToZero() {
   if (!is_initialized_)
     return;
   system_brightness_ = 0;
   if (backlight_->SetBrightness(0))
     WritePrefs();
 }
 
-gboolean BacklightController::DisplayOffWhenBacklightOff() {
-  int64 brightness = 0;
-  CHECK(GetBrightness(&brightness));
-  if (brightness == 0) {
+void BacklightController::TurnScreenOff() {
+  if (state_ == BACKLIGHT_IDLE_OFF && GDK_DISPLAY() != NULL)
     CHECK(DPMSForceLevel(GDK_DISPLAY(), DPMSModeOff));
-    return false;
-  } else {
-    // If the brightness has not been set all the way down, keep polling it
-    // until it reaches zero.
-    return true;
-  }
 }
 
+
 }  // namespace power_manager