Animations: Introduce compositor AnimationPlayer and AnimationTimeline.

Source/core/animation/AnimationTimeline.cpp

Index: Source/core/animation/AnimationTimeline.cpp
diff --git a/Source/core/animation/AnimationTimeline.cpp b/Source/core/animation/AnimationTimeline.cpp
index a9d7abfda6e1e39ed1396850c8a7cf600371b5d1..5234d2b60f304fb88aa5011d1422dcb546cc220a 100644
--- a/Source/core/animation/AnimationTimeline.cpp
+++ b/Source/core/animation/AnimationTimeline.cpp
@@ -37,7 +37,11 @@
 #include "core/frame/FrameView.h"
 #include "core/loader/DocumentLoader.h"
 #include "core/page/Page.h"
+#include "platform/RuntimeEnabledFeatures.h"
 #include "platform/TraceEvent.h"
+#include "public/platform/Platform.h"
+#include "public/platform/WebCompositorAnimationTimeline.h"
+#include "public/platform/WebCompositorSupport.h"
 
 namespace blink {
 
@@ -72,6 +76,9 @@ AnimationTimeline::AnimationTimeline(Document* document, PassOwnPtrWillBeRawPtr<
     else
         m_timing = timing;
 
+    if (RuntimeEnabledFeatures::compositorAnimationTimelinesEnabled() && Platform::current()->compositorSupport())
+        m_compositorTimeline = adoptPtr(Platform::current()->compositorSupport()->createAnimationTimeline());
+
     ASSERT(document);
 }