Get rid of the ability to unregister preferences.

base/prefs/pref_registry.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_PREF_REGISTRY_H_
 #define BASE_PREFS_PREF_REGISTRY_H_
 
 #include "base/callback.h"
 #include "base/memory/ref_counted.h"
 #include "base/prefs/base_prefs_export.h"
@@ skipping 12 matching lines @@
 // The way you use a PrefRegistry is that you register all required
 // preferences on it (via one of its subclasses), then pass it as a
 // construction parameter to PrefService.
 //
 // Currently, registrations after constructing the PrefService will
 // also work, but this is being deprecated.
 class BASE_PREFS_EXPORT PrefRegistry : public base::RefCounted<PrefRegistry> {
  public:
   typedef PrefValueMap::const_iterator const_iterator;
   typedef base::Callback<void(const char*, base::Value*)> RegistrationCallback;
-  typedef base::Callback<void(const char*)> UnregistrationCallback;
 
   PrefRegistry();
 
   // Gets the registered defaults.
   scoped_refptr<PrefStore> defaults();
 
   // Allows iteration over defaults.
   const_iterator begin() const;
   const_iterator end() const;
 
-  // Exactly one callback can be set for each of two events:
-  // Registration and unregistration. If either is set, the callback
-  // will be invoked each time registration and/or unregistration has
-  // been performed on this object.
+  // Exactly one callback can be set for registration. The callback
+  // will be invoked each time registration has been performed on this
+  // object.
   //
-  // Calling either of these methods after a callback has already been
-  // set will make the object forget the previous callback and use the
-  // new one instead.
+  // Calling this method after a callback has already been set will
+  // make the object forget the previous callback and use the new one
+  // instead.
   void SetRegistrationCallback(const RegistrationCallback& callback);
-  void SetUnregistrationCallback(const UnregistrationCallback& callback);
-
-  // Unregisters a preference. This is going away soon.
-  void DeprecatedUnregisterPreference(const char* path);
 
  protected:
   friend class base::RefCounted<PrefRegistry>;
   virtual ~PrefRegistry();
 
   // Used by subclasses to register a default value for a preference.
   void RegisterPreference(const char* path, base::Value* default_value);
 
   scoped_refptr<DefaultPrefStore> defaults_;
 
  private:
   RegistrationCallback registration_callback_;
-  UnregistrationCallback unregistration_callback_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefRegistry);
 };
 
 #endif  // BASE_PREFS_PREF_REGISTRY_H_