Make SyncStartupTracker::Observer destructor virtual

chrome/browser/sync/sync_startup_tracker.h

 // 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 CHROME_BROWSER_SYNC_SYNC_STARTUP_TRACKER_H_
 #define CHROME_BROWSER_SYNC_SYNC_STARTUP_TRACKER_H_
 
 #include "base/basictypes.h"
 #include "base/compiler_specific.h"
 #include "chrome/browser/sync/profile_sync_service_observer.h"
 
 class Profile;
 
 // SyncStartupTracker provides a centralized way for observers to detect when
 // ProfileSyncService has successfully started up, or when startup has failed
 // due to some kind of error. This code was originally part of SigninTracker
 // but now that sync initialization is no longer a required part of signin,
 // it has been broken out of that class so only those places that care about
 // sync initialization depend on it.
 class SyncStartupTracker : public ProfileSyncServiceObserver {
  public:
   // Observer interface used to notify observers when sync has started up.
   class Observer {
    public:
+    virtual ~Observer() {}
+
     virtual void SyncStartupCompleted() = 0;
     virtual void SyncStartupFailed() = 0;
   };
 
   SyncStartupTracker(Profile* profile, Observer* observer);
   virtual ~SyncStartupTracker();
 
   enum SyncServiceState {
     // Sync backend is still starting up.
     SYNC_STARTUP_PENDING,
@@ skipping 20 matching lines @@
   // Profile whose ProfileSyncService we should track.
   Profile* profile_;
 
   // Weak pointer to the observer to notify.
   Observer* observer_;
 
   DISALLOW_COPY_AND_ASSIGN(SyncStartupTracker);
 };
 
 #endif  // CHROME_BROWSER_SYNC_SYNC_STARTUP_TRACKER_H_