Add fade to white animation when power button is pressed on Athena

athena/screen/public/screen_manager.h

Index: athena/screen/public/screen_manager.h
diff --git a/athena/screen/public/screen_manager.h b/athena/screen/public/screen_manager.h
index 8a82f6c617272a0b59d7d527e61894dd5d3fcd4a..82ad85592bf7067f2b44a9bbddb58f9ac7b17d7f 100644
--- a/athena/screen/public/screen_manager.h
+++ b/athena/screen/public/screen_manager.h
@@ -17,6 +17,10 @@ namespace gfx {
 class ImageSkia;
 }
 
+namespace ui {
+class LayerAnimator;
+}
+
 namespace wm {
 class FocusRules;
 }
@@ -64,6 +68,10 @@ class ATHENA_EXPORT ScreenManager {
   // Sets the background image.
   virtual void SetBackgroundImage(const gfx::ImageSkia& image) = 0;
 
+  // Returns the LayerAnimator to use to animate the entire screen (e.g. fade
+  // screen to white).
+  virtual ui::LayerAnimator* GetScreenAnimator() = 0;
+
   // Create a focus rules.
   // TODO(oshima): Make this virtual function.
   static wm::FocusRules* CreateFocusRules();