Remove content::NotificationObserver dependency from most Prefs code.

chrome/chrome_browser.gypi

 # 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.
 
 {
   'targets': [
     {
       'target_name': 'browser',
       'type': 'static_library',
@@ skipping 2150 matching lines @@
         # This file is generated by the autofill_regexes action.
         '<(SHARED_INTERMEDIATE_DIR)/autofill_regex_constants.cc',
 
         # TODO(joi): Move to 'base_prefs' target in base/base.gyp once
         # Prefs move is complete and dependencies have been broken.
         '../base/prefs/default_pref_store.cc',
         '../base/prefs/default_pref_store.h',
         '../base/prefs/overlay_user_pref_store.cc',
         '../base/prefs/overlay_user_pref_store.h',
         '../base/prefs/pref_notifier.h',
+        '../base/prefs/pref_observer.h',
+        '../base/prefs/pref_init_observer.h',
         '../base/prefs/pref_value_map.cc',
         '../base/prefs/pref_value_map.h',
         '../base/prefs/public/pref_change_registrar.cc',
         '../base/prefs/public/pref_change_registrar.h',
         '../base/prefs/public/pref_service_base.h',
         '../base/prefs/value_map_pref_store.cc',
         '../base/prefs/value_map_pref_store.h',
       ],
       'conditions': [
         ['enable_one_click_signin==0', {
@@ skipping 764 matching lines @@
             'proto_in_dir': '../third_party/cros_system_api/dbus',
             'proto_out_dir': 'chrome/browser/media_transfer_protocol',
           },
           'includes': ['../build/protoc.gypi'],
         },
       ],
      },
     ],
   ],
 }