Animations: Introduce compositor AnimationPlayer and AnimationTimeline.

Source/core/animation/Animation.h

Index: Source/core/animation/Animation.h
diff --git a/Source/core/animation/Animation.h b/Source/core/animation/Animation.h
index ae2be2b890e64649f3019a1d773375bc9759f2f6..69b4692f2c3738bb36a94da35f0665a68fd634f2 100644
--- a/Source/core/animation/Animation.h
+++ b/Source/core/animation/Animation.h
@@ -82,6 +82,9 @@ public:
     void cancelIncompatibleAnimationsOnCompositor();
     void pauseAnimationForTestingOnCompositor(double pauseTime);
 
+    bool canAttachCompositedLayers() const;
+    void attachCompositedLayers();
+
     void setCompositorAnimationIdsForTesting(const Vector<int>& compositorAnimationIds) { m_compositorAnimationIds = compositorAnimationIds; }
 
     DECLARE_VIRTUAL_TRACE();