FBTF: Move the TabRestoreService::Observer into its own file.

chrome/browser/sessions/tab_restore_service_observer.h

+// Copyright (c) 2010 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 CHROME_BROWSER_SESSIONS_TAB_RESTORE_SERVICE_OBSERVER_H_
+#define CHROME_BROWSER_SESSIONS_TAB_RESTORE_SERVICE_OBSERVER_H_
+
+class TabRestoreService;
+
+// Observer is notified when the set of entries managed by TabRestoreService
+// changes in some way.
+class TabRestoreServiceObserver {
+ public:
+  // Sent when the set of entries changes in some way.
+  virtual void TabRestoreServiceChanged(TabRestoreService* service) = 0;
+
+  // Sent to all remaining Observers when TabRestoreService's
+  // destructor is run.
+  virtual void TabRestoreServiceDestroyed(TabRestoreService* service) = 0;
+
+ protected:
+  virtual ~TabRestoreServiceObserver() {}
+};
+
+#endif  // CHROME_BROWSER_SESSIONS_TAB_RESTORE_SERVICE_OBSERVER_H_