Animations: Introduce compositor AnimationPlayer and AnimationTimeline.

Source/core/animation/AnimationTimeline.h

Index: Source/core/animation/AnimationTimeline.h
diff --git a/Source/core/animation/AnimationTimeline.h b/Source/core/animation/AnimationTimeline.h
index badad7c28c761dea0c45da560778fdd6c80e4edf..c995bf881ce00f750afda1349286bb1be2bd91e8 100644
--- a/Source/core/animation/AnimationTimeline.h
+++ b/Source/core/animation/AnimationTimeline.h
@@ -37,6 +37,7 @@
 #include "core/dom/Element.h"
 #include "platform/Timer.h"
 #include "platform/heap/Handle.h"
+#include "public/platform/WebCompositorAnimationTimeline.h"
 #include "wtf/RefCounted.h"
 #include "wtf/RefPtr.h"
 #include "wtf/Vector.h"
@@ -97,6 +98,9 @@ public:
     void setPlaybackRate(double);
     double playbackRate() const;
 
+    WebCompositorAnimationTimeline* compositorTimeline() const { return m_compositorTimeline.get(); }
+    void updateCompositedLayersAttachments();
+
     Document* document() { return m_document.get(); }
 #if !ENABLE(OILPAN)
     void detachFromDocument();
@@ -125,6 +129,8 @@ private:
     OwnPtrWillBeMember<PlatformTiming> m_timing;
     double m_lastCurrentTimeInternal;
 
+    OwnPtr<WebCompositorAnimationTimeline> m_compositorTimeline;
+
     class AnimationTimelineTiming final : public PlatformTiming {
     public:
         AnimationTimelineTiming(AnimationTimeline* timeline)