Add ability to change default pref values, and use in BrowserInstantController.

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 22 matching lines @@
 
   PrefRegistry();
 
   // Gets the registered defaults.
   scoped_refptr<PrefStore> defaults();
 
   // Allows iteration over defaults.
   const_iterator begin() const;
   const_iterator end() const;
 
+  // Changes the default value for a preference. Takes ownership of |value|.
+  //
+  // |pref_name| must be a previously registered preference.
+  void SetDefaultPrefValue(const char* pref_name, base::Value* value);
+
   // Exactly one callback can be set for registration. The callback
   // will be invoked each time registration has been performed on this
   // object.
   //
   // 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);
 
  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_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefRegistry);
 };
 
 #endif  // BASE_PREFS_PREF_REGISTRY_H_