views: Some more layer change, and add/update some tests for layers.

ui/aura/window_delegate.h

Index: ui/aura/window_delegate.h
diff --git a/ui/aura/window_delegate.h b/ui/aura/window_delegate.h
index 3e81515b1950ffc9b60268b10ba9cb47fd7856db..928f1645778a4e5b0b7461cc6506359bc2a89d94 100644
--- a/ui/aura/window_delegate.h
+++ b/ui/aura/window_delegate.h
@@ -70,6 +70,9 @@ class AURA_EXPORT WindowDelegate {
   // The delegate can use this as an opportunity to delete itself if necessary.
   virtual void OnWindowDestroyed() = 0;
 
+  // Called when the visibility of a Window changed.
+  virtual void OnWindowVisibilityChanged(bool visible) = 0;
+
  protected:
   virtual ~WindowDelegate() {}
 };