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
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+++ b/cc/animation_registrar.h
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+// 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;
+
+// TODO(vollick): we need to rename:
+//    AnimationRegistrar -> AnimationController
+//    LayerAnimationController -> LayerAnimator
+class CC_EXPORT AnimationRegistrar {
+ public:
+  // Registers the given animation controller as active. An active animation
+  // controller is one that has a running animation that needs to be ticked.
+  virtual void DidActivateAnimationController(LayerAnimationController*) = 0;
+
+  // Unregisters the given animation controller. When this happens, the
+  // animation controller will no longer be ticked (since it's not active). It
+  // is not an error to call this function with a deactivated controller.
+  virtual void DidDeactivateAnimationController(LayerAnimationController*) = 0;
+
+  // Registers the given controller as alive.
+  virtual void RegisterAnimationController(LayerAnimationController*) = 0;
+
+  // Unregisters the given controller as alive.
+  virtual void UnregisterAnimationController(LayerAnimationController*) = 0;
+};
+
+}  // namespace cc
+
+#endif  // CC_ANIMATION_REGISTRAR_H_