Listen to Display reconfiguration and notify DisplayObservers on Mac.

ui/gfx/display_change_notifier.h

Index: ui/gfx/display_change_notifier.h
diff --git a/ui/gfx/display_change_notifier.h b/ui/gfx/display_change_notifier.h
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+++ b/ui/gfx/display_change_notifier.h
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+// 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_GFX_DISPLAY_CHANGE_NOTIFIER_H_
+#define UI_GFX_DISPLAY_CHANGE_NOTIFIER_H_
+
+#include <vector>
+
+#include "base/observer_list.h"
+#include "ui/gfx/gfx_export.h"
+
+namespace gfx {
+
+class Display;
+class DisplayObserver;
+
+// DisplayChangeNotifier is a class implementing the handling of DisplayObserver
+// notification for Screen.
+class GFX_EXPORT DisplayChangeNotifier {
+ public:
+  DisplayChangeNotifier();
+  ~DisplayChangeNotifier();
+
+  void AddObserver(DisplayObserver* observer);
+
+  void RemoveObserver(DisplayObserver* observer);
+
+  void NotifyDisplaysChanged(const std::vector<Display>& old_displays,
+                             const std::vector<Display>& new_displays);
+
+ private:
+  // The observers that need to be notified when a display is modified, added
+  // or removed.
+  ObserverList<DisplayObserver> observer_list_;
+
+  DISALLOW_COPY_AND_ASSIGN(DisplayChangeNotifier);
+};
+
+} // namespace gfx
+
+#endif // UI_GFX_DISPLAY_CHANGE_NOTIFIER_H_
+