Use an auxiliary list of animation controllers.

cc/layer_tree_host.h

Index: cc/layer_tree_host.h
diff --git a/cc/layer_tree_host.h b/cc/layer_tree_host.h
index c140b31da21635175b86a2af5fa22821654a8db0..85b869af28bf9612d61189569d291c767aec9021 100644
--- a/cc/layer_tree_host.h
+++ b/cc/layer_tree_host.h
@@ -14,6 +14,7 @@
 #include "base/memory/scoped_ptr.h"
 #include "base/time.h"
 #include "cc/animation_events.h"
+#include "cc/animation_registrar.h"
 #include "cc/cc_export.h"
 #include "cc/graphics_context.h"
 #include "cc/layer_tree_host_client.h"
@@ -36,6 +37,15 @@ struct hash<WebKit::WebGraphicsContext3D*> {
   }
 };
 } // namespace BASE_HASH_NAMESPACE
+
+namespace BASE_HASH_NAMESPACE {
+template<>
+struct hash<cc::LayerAnimationController*> {
+  size_t operator()(cc::LayerAnimationController* ptr) const {
+    return hash<size_t>()(reinterpret_cast<size_t>(ptr));
+  }
+};
+} // namespace BASE_HASH_NAMESPACE
 #endif // COMPILER
 
 namespace cc {
@@ -99,7 +109,8 @@ struct CC_EXPORT RendererCapabilities {
     int maxTextureSize;
 };
 
-class CC_EXPORT LayerTreeHost : public RateLimiterClient {
+class CC_EXPORT LayerTreeHost : public RateLimiterClient,
+                                public AnimationRegistrar {
 public:
     static scoped_ptr<LayerTreeHost> create(LayerTreeHostClient*, const LayerTreeSettings&, scoped_ptr<Thread> implThread);
     virtual ~LayerTreeHost();
@@ -175,7 +186,6 @@ public:
     bool commitRequested() const;
 
     void setAnimationEvents(scoped_ptr<AnimationEventsVector>, base::Time wallClockTime);
-    virtual void didAddAnimation();
 
     Layer* rootLayer() { return m_rootLayer.get(); }
     const Layer* rootLayer() const { return m_rootLayer.get(); }
@@ -232,8 +242,13 @@ protected:
     LayerTreeHost(LayerTreeHostClient*, const LayerTreeSettings&);
     bool initialize(scoped_ptr<Thread> implThread);
 
+    // AnimationRegistar implementation.

[nduca, 2012/12/04 05:40:26]

so, walk me through the benefit of this being LTH rather than ref-counted
global?

+    virtual void Register(LayerAnimationController*) OVERRIDE;
+    virtual void Unregister(LayerAnimationController*) OVERRIDE;
+
 private:
     typedef std::vector<scoped_refptr<Layer> > LayerList;
+    typedef base::hash_set<LayerAnimationController*> AnimationControllerSet;
 
     void initializeRenderer();
 
@@ -256,7 +271,6 @@ private:
     void createHUDLayerIfNeeded();
 
     bool m_animating;
-    bool m_needsAnimateLayers;
 
     base::CancelableClosure m_prepaintCallback;
 
@@ -301,6 +315,8 @@ private:
 
     static bool s_needsFilterContext;
 
+    AnimationControllerSet m_activeAnimationControllers;
+
     DISALLOW_COPY_AND_ASSIGN(LayerTreeHost);
 };