Fix stale compositor references from ui::Layer

ui/gfx/compositor/layer.h

Index: ui/gfx/compositor/layer.h
diff --git a/ui/gfx/compositor/layer.h b/ui/gfx/compositor/layer.h
index d8cb66cda744febc786d69821ee63cc8ed7fa553..76fef3e99cc4d9af65fb1d4f31f73608b02ef9c2 100644
--- a/ui/gfx/compositor/layer.h
+++ b/ui/gfx/compositor/layer.h
@@ -48,10 +48,8 @@ class COMPOSITOR_EXPORT Layer :
     LAYER_HAS_TEXTURE = 1
   };
 
-  // |compositor| can be NULL, and will be set later when the Layer is added to
-  // a Compositor.
-  explicit Layer(Compositor* compositor);
-  Layer(Compositor* compositor, LayerType type);
+  Layer();
+  explicit Layer(LayerType type);
   virtual ~Layer();
 
   // Retrieves the Layer's compositor. The Layer will walk up its parent chain
@@ -152,10 +150,6 @@ class COMPOSITOR_EXPORT Layer :
 
   const gfx::Rect& hole_rect() const {  return hole_rect_; }
 
-  // The compositor.
-  const Compositor* compositor() const { return compositor_; }
-  Compositor* compositor() { return compositor_; }
-
   const ui::Texture* texture() const { return texture_.get(); }
 
   // |texture| cannot be NULL, and this function cannot be called more than