Use an auxiliary list of animation controllers.

cc/animation_registrar.h

Index: cc/animation_registrar.h
diff --git a/cc/animation_registrar.h b/cc/animation_registrar.h
new file mode 100644
index 0000000000000000000000000000000000000000..7dbf2223446dbcbcc712f77b41429bd21fc75e01
--- /dev/null
+++ b/cc/animation_registrar.h
@@ -0,0 +1,20 @@
+// Copyright 2012 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef CC_ANIMATION_REGISTRAR_H_
+#define CC_ANIMATION_REGISTRAR_H_
+
+namespace cc {
+
+class LayerAnimationController;
+
+class CC_EXPORT AnimationRegistrar {
+ public:
+  virtual void Register(LayerAnimationController*) = 0;
+  virtual void Unregister(LayerAnimationController*) = 0;
+};
+
+}  // namespace cc
+
+#endif  // CC_ANIMATION_REGISTRAR_H_