Fix black background when locking with fullscreen window:

ui/base/animation/animation_container.h

Index: ui/base/animation/animation_container.h
diff --git a/ui/base/animation/animation_container.h b/ui/base/animation/animation_container.h
index 89f6392392402fbc8151fb4165d5e59c366d86ac..e88c3d27445fc83d62af640378a5be0a10bcbbb2 100644
--- a/ui/base/animation/animation_container.h
+++ b/ui/base/animation/animation_container.h
@@ -17,6 +17,10 @@ namespace ui {
 class AnimationContainerElement;
 class AnimationContainerObserver;
 
+namespace test {
+class AnimationContainerTestHelper;
+}
+
 // AnimationContainer is used by Animation to manage the underlying timer.
 // Internally each Animation creates a single AnimationContainer. You can
 // group a set of Animations into the same AnimationContainer by way of
@@ -53,6 +57,7 @@ class UI_EXPORT AnimationContainer
 
  private:
   friend class base::RefCounted<AnimationContainer>;
+  friend class test::AnimationContainerTestHelper;
 
   typedef std::set<AnimationContainerElement*> Elements;