Add observers list for NativeWindow.

browser/native_window_observer.h

@@ -0,0 +1,23 @@
+// Copyright (c) 2013 GitHub, Inc. All rights reserved.
+// Use of this source code is governed by a BSD-style license that can be
+// found in the LICENSE file.
+
+#ifndef ATOM_BROWSER_NATIVE_WINDOW_OBSERVER_H_
+#define ATOM_BROWSER_NATIVE_WINDOW_OBSERVER_H_
+
+#include <iosfwd>
+
+namespace atom {
+
+class NativeWindowObserver {
+ public:
+  virtual ~NativeWindowObserver() {};
+
+  // Called when the web page of the window has updated it's document title.
+  virtual void OnPageTitleUpdated(bool* prevent_default,
+                                  const std::string& title) = 0;
+};
+
+}  // namespace atom
+
+#endif  // ATOM_BROWSER_NATIVE_WINDOW_OBSERVER_H_