Animations: Introduce compositor AnimationPlayer and AnimationTimeline.

Source/web/WebViewImpl.h

Index: Source/web/WebViewImpl.h
diff --git a/Source/web/WebViewImpl.h b/Source/web/WebViewImpl.h
index 4ce6a4603857e9bbcf8c8323055597b27ba6c2ab..1b931b6e79c8e4c5397bac18ec9f95c88d76aef2 100644
--- a/Source/web/WebViewImpl.h
+++ b/Source/web/WebViewImpl.h
@@ -75,6 +75,7 @@ class PopupContainer;
 class LayerCompositor;
 class UserGestureToken;
 class WebActiveGestureAnimation;
+class WebCompositorAnimationTimeline;
 class WebDevToolsAgentImpl;
 class WebLayerTreeView;
 class WebLocalFrameImpl;
@@ -440,6 +441,7 @@ public:
     LayerCompositor* compositor() const;
     void registerForAnimations(WebLayer*);
     void scheduleAnimation();
+    void setCompositorAnimationTimeline(WebCompositorAnimationTimeline*);
 
     virtual void setVisibilityState(WebPageVisibilityState, bool) override;