Revert of Delete base/prefs and update callers to use components.

components/prefs/pref_observer.h

 // Copyright (c) 2012 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 COMPONENTS_PREFS_PREF_OBSERVER_H_
-#define COMPONENTS_PREFS_PREF_OBSERVER_H_
+#ifndef BASE_PREFS_PREF_OBSERVER_H_
+#define BASE_PREFS_PREF_OBSERVER_H_
 
 #include <string>
 
 class PrefService;
 
 // Used internally to the Prefs subsystem to pass preference change
 // notifications between PrefService, PrefNotifierImpl and
 // PrefChangeRegistrar.
 class PrefObserver {
  public:
   virtual void OnPreferenceChanged(PrefService* service,
                                    const std::string& pref_name) = 0;
 };
 
-#endif  // COMPONENTS_PREFS_PREF_OBSERVER_H_
+#endif  // BASE_PREFS_PREF_OBSERVER_H_