Add brightness/grayscale animations and use them for OOBE boot transition

ash/wm/window_animations.h

Index: ash/wm/window_animations.h
diff --git a/ash/wm/window_animations.h b/ash/wm/window_animations.h
index 9a156bf3eb87fa9114e0298fae000883b7c94b21..0705143192b67b94f3b7ebabcb7d73a41dc068c6 100644
--- a/ash/wm/window_animations.h
+++ b/ash/wm/window_animations.h
@@ -35,6 +35,8 @@ enum WindowVisibilityAnimationType {
   WINDOW_VISIBILITY_ANIMATION_TYPE_WORKSPACE_HIDE,  // Inverse of SHOW.
   WINDOW_VISIBILITY_ANIMATION_TYPE_MINIMIZE,        // Window scale/rotates down
                                                     // to its launcher icon.
+  // Fade in/out using brightness and grayscale web filters.
+  WINDOW_VISIBILITY_ANIMATION_TYPE_BRIGHTNESS_GRAYSCALE,
 };
 
 // Type of visibility change transition that a window should animate.