Remove content::NotificationObserver dependency from most Prefs code.

base/prefs/persistent_pref_store.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 BASE_PREFS_PERSISTENT_PREF_STORE_H_
 #define BASE_PREFS_PERSISTENT_PREF_STORE_H_
 
 #include <string>
 
+#include "base/prefs/base_prefs_export.h"
 #include "base/prefs/pref_store.h"
 
 // This interface is complementary to the PrefStore interface, declaring
 // additional functionality that adds support for setting values and persisting
 // the data to some backing store.
-class PersistentPrefStore : public PrefStore {
+class BASE_PREFS_EXPORT PersistentPrefStore : public PrefStore {
  public:
   // Unique integer code for each type of error so we can report them
   // distinctly in a histogram.
   // NOTE: Don't change the order here as it will change the server's meaning
   // of the histogram.
   enum PrefReadError {
     PREF_READ_ERROR_NONE = 0,
     PREF_READ_ERROR_JSON_PARSE,
     PREF_READ_ERROR_JSON_TYPE,
     PREF_READ_ERROR_ACCESS_DENIED,
@@ skipping 59 matching lines @@
   virtual void ReadPrefsAsync(ReadErrorDelegate* error_delegate) = 0;
 
   // Lands any pending writes to disk.
   virtual void CommitPendingWrite() = 0;
 
  protected:
   virtual ~PersistentPrefStore() {}
 };
 
 #endif  // BASE_PREFS_PERSISTENT_PREF_STORE_H_