Moves transient window observer methods out of WindowObserver

ui/views/corewm/transient_window_observer.h

+// Copyright 2014 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_COREWM_TRANSIENT_WINDOW_OBSERVER_H_
+#define UI_VIEWS_COREWM_TRANSIENT_WINDOW_OBSERVER_H_
+
+#include "ui/views/views_export.h"
+
+namespace aura {
+class Window;
+}
+
+namespace views {
+namespace corewm {
+
+class VIEWS_EXPORT TransientWindowObserver {
+ public:
+  // Called when a transient child is added to |window|.
+  virtual void OnTransientChildAdded(aura::Window* window,
+                                     aura::Window* transient) = 0;
+
+  // Called when a transient child is removed from |window|.
+  virtual void OnTransientChildRemoved(aura::Window* window,
+                                       aura::Window* transient) = 0;
+
+ protected:
+  virtual ~TransientWindowObserver() {}
+};
+
+}  // namespace corewm
+}  // namespace views
+
+#endif  // UI_VIEWS_COREWM_TRANSIENT_WINDOW_OBSERVER_H_