Reorder the NativeViews attached to a view via kViewHostKey according to the position of the view

ui/views/widget/window_reorderer.h

Index: ui/views/widget/window_reorderer.h
diff --git a/ui/views/widget/window_reorderer.h b/ui/views/widget/window_reorderer.h
new file mode 100644
index 0000000000000000000000000000000000000000..6fc0c313ef096661d231f8cba07c8d65afa52ac0
--- /dev/null
+++ b/ui/views/widget/window_reorderer.h
@@ -0,0 +1,59 @@
+// Copyright (c) 2013 The Chromium Authors. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef UI_VIEWS_WIDGET_WINDOW_REORDERER_H_
+#define UI_VIEWS_WIDGET_WINDOW_REORDERER_H_
+
+#include "base/compiler_specific.h"
+#include "base/memory/scoped_ptr.h"
+#include "ui/aura/window_observer.h"
+
+namespace aura {
+class Window;
+}
+
+namespace views {
+class View;
+
+// Class which reorders the widget's child windows which have an associated view
+// in the widget's view tree according the z-order of the views in the view
+// tree. Windows not associated to a view are stacked above windows with an
+// associated view. The child windows' layers are additionally reordered
+// according to the z-order of the associated views relative to views with
+// layers.
+class WindowReorderer : public aura::WindowObserver {
+ public:
+  WindowReorderer(aura::Window* window, View* root_view);
+  virtual ~WindowReorderer();
+
+  // Explicitly reorder the children of |window_| (and their layers). This
+  // method should be called when the position of a view with an associated
+  // window changes in the view hierarchy. This method assumes that the
+  // child layers of |window_| which are owned by views are already in the
+  // correct z-order relative to each other and does no reordering if there
+  // are no views with an associated window.
+  void ReorderChildWindows();
+
+ private:
+  // aura::WindowObserver overrides:
+  virtual void OnWindowAdded(aura::Window* new_window) OVERRIDE;
+  virtual void OnWillRemoveWindow(aura::Window* window) OVERRIDE;
+  virtual void OnWindowDestroying(aura::Window* window) OVERRIDE;
+
+  // The window and the root view of the native widget which owns the
+  // WindowReorderer.
+  aura::Window* parent_window_;
+  View* root_view_;
+
+  // Reorders windows as a result of the kHostViewKey being set on a child of
+  // |parent_window_|.
+  class AssociationObserver;
+  scoped_ptr<AssociationObserver> association_observer_;
+
+  DISALLOW_COPY_AND_ASSIGN(WindowReorderer);
+};
+
+}  // namespace views
+
+#endif  // UI_VIEWS_WIDGET_WINDOW_REORDERER_H_