chromeos: Add support for dimming the screen.

chromeos/dbus/power_manager_client.h

Index: chromeos/dbus/power_manager_client.h
diff --git a/chromeos/dbus/power_manager_client.h b/chromeos/dbus/power_manager_client.h
index eb199474ee877ed986b9f6bd4512279f724202bd..00c27b83007f785056948c878fbfc241e531e300 100644
--- a/chromeos/dbus/power_manager_client.h
+++ b/chromeos/dbus/power_manager_client.h
@@ -39,6 +39,11 @@ class CHROMEOS_EXPORT PowerManagerClient {
   // Interface for observing changes from the power manager.
   class Observer {
    public:
+    enum ScreenDimmingState {
+      SCREEN_DIMMING_NONE = 0,
+      SCREEN_DIMMING_IDLE,
+    };
+
     virtual ~Observer() {}
 
     // Called when the brightness is changed.
@@ -75,6 +80,10 @@ class CHROMEOS_EXPORT PowerManagerClient {
 
     // Called when we go from idle to active.
     virtual void ActiveNotify() {}
+
+    // Called when a request is received to dim or undim the screen in software
+    // (as opposed to the more-common method of adjusting the backlight).
+    virtual void ScreenDimmingRequested(ScreenDimmingState state) {}
   };
 
   enum UpdateRequestType {