Change Window visibility to a simple boolean for now.

ui/aura/desktop.cc

Index: ui/aura/desktop.cc
===================================================================
--- ui/aura/desktop.cc	(revision 103502)
+++ ui/aura/desktop.cc	(working copy)
@@ -57,7 +57,7 @@
   Window* default_parent = new internal::ToplevelWindowContainer;
   default_parent->Init();
   default_parent->SetBounds(window_->bounds());
-  default_parent->SetVisibility(Window::VISIBILITY_SHOWN);
+  default_parent->Show();
   window_->AddChild(default_parent);
   set_default_parent(default_parent);
 }
@@ -136,7 +136,7 @@
   Window::Windows windows(default_parent_->children());
   for (Window::Windows::const_reverse_iterator i = windows.rbegin();
        i != windows.rend(); ++i) {
-    if (*i != ignore && (*i)->visibility() == Window::VISIBILITY_SHOWN &&
+    if (*i != ignore && (*i)->visible() &&
         (*i)->delegate()->ShouldActivate(NULL))
       return *i;
   }