Fix black background when locking with fullscreen window:

ui/compositor/layer_animator.h

Index: ui/compositor/layer_animator.h
diff --git a/ui/compositor/layer_animator.h b/ui/compositor/layer_animator.h
index 6c24008cb0d7698e1cb2ecca9d43bd3de14a8244..43a43ff5d1e47be0e05e438f36ffb3f3b0149def 100644
--- a/ui/compositor/layer_animator.h
+++ b/ui/compositor/layer_animator.h
@@ -14,6 +14,7 @@
 #include "base/observer_list.h"
 #include "base/time.h"
 #include "ui/base/animation/animation_container_element.h"
+#include "ui/base/animation/animation_container_test_helper.h"
 #include "ui/base/animation/tween.h"
 #include "ui/compositor/compositor_export.h"
 #include "ui/compositor/layer_animation_element.h"
@@ -31,6 +32,13 @@ class LayerAnimationDelegate;
 class LayerAnimationObserver;
 class ScopedLayerAnimationSettings;
 
+namespace internal {
+
+// Returns the AnimationContainer we're added to.
+COMPOSITOR_EXPORT ui::AnimationContainer* GetLayerAnimationContainer();
+
+} // namespace internal
+
 // When a property of layer needs to be changed it is set by way of
 // LayerAnimator. This enables LayerAnimator to animate property changes.
 // NB: during many tests, set_disable_animations_for_test is used and causes