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

ash/shell.cc

Index: ash/shell.cc
diff --git a/ash/shell.cc b/ash/shell.cc
index 77678e09dcaedb641cbb281d1f6b75f51593d4ee..c9becb3c0b87de17c1f0e96ff152a77e942268b9 100644
--- a/ash/shell.cc
+++ b/ash/shell.cc
@@ -117,6 +117,10 @@ class DummyUserWallpaperDelegate : public UserWallpaperDelegate {
 
   virtual ~DummyUserWallpaperDelegate() {}
 
+  virtual ash::WindowVisibilityAnimationType GetAnimationType() OVERRIDE {
+    return WINDOW_VISIBILITY_ANIMATION_TYPE_FADE;
+  }
+
   virtual void InitializeWallpaper() OVERRIDE {
     ash::Shell::GetInstance()->desktop_background_controller()->
         CreateEmptyWallpaper();