Use WebKit compositor in ui::Layer

ui/gfx/compositor/compositor.h

Index: ui/gfx/compositor/compositor.h
diff --git a/ui/gfx/compositor/compositor.h b/ui/gfx/compositor/compositor.h
index 1251b6a42108ed2a00474e3e958b400244aedbe0..574fed88f87ce3475fa21732ef5c79a91b478556 100644
--- a/ui/gfx/compositor/compositor.h
+++ b/ui/gfx/compositor/compositor.h
@@ -107,9 +107,7 @@ class COMPOSITOR_EXPORT Compositor : public base::RefCounted<Compositor> {
   virtual void Blur(const gfx::Rect& bounds) = 0;
 
   // Schedules a redraw of the layer tree associated with this compositor.
-  void ScheduleDraw() {
-    delegate_->ScheduleDraw();
-  }
+  virtual void ScheduleDraw();
 
   // Sets the root of the layer tree drawn by this Compositor.
   // The Compositor does not own the root layer.
@@ -150,6 +148,8 @@ class COMPOSITOR_EXPORT Compositor : public base::RefCounted<Compositor> {
   virtual void OnNotifyEnd() = 0;
 
   virtual void OnWidgetSizeChanged() = 0;
+  virtual void OnRootLayerChanged();
+  virtual void DrawTree();
 
   CompositorDelegate* delegate() { return delegate_; }