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 6048f2b8211a0eb431bd280068b608df9fd21025..168688ba98ed41f10499840a0084a483f1a5e32c 100644
--- a/Source/web/WebViewImpl.h
+++ b/Source/web/WebViewImpl.h
@@ -76,6 +76,7 @@ class LayerCompositor;
 class TopControls;
 class UserGestureToken;
 class WebActiveGestureAnimation;
+class WebCompositorAnimationTimeline;
 class WebDevToolsAgentImpl;
 class WebLayerTreeView;
 class WebLocalFrameImpl;
@@ -443,6 +444,7 @@ public:
     LayerCompositor* compositor() const;
     void registerForAnimations(WebLayer*);
     void scheduleAnimation();
+    void setCompositorAnimationTimeline(WebCompositorAnimationTimeline*);
 
     virtual void setVisibilityState(WebPageVisibilityState, bool) override;