Adjust preference sync code to only sync user modifiable preferences.

chrome/browser/pref_service.h

 // Copyright (c) 2010 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.
 
 // This provides a way to access the application's current preferences.
 
 #ifndef CHROME_BROWSER_PREF_SERVICE_H_
 #define CHROME_BROWSER_PREF_SERVICE_H_
 
 #include <set>
@@ skipping 55 matching lines @@
     bool HasUserSetting() const;
 
     // Returns true if the Preference value is currently being controlled by an
     // extension, and not by any higher-priority source.
     bool IsExtensionControlled() const;
 
     // Returns true if the Preference value is currently being controlled by a
     // user setting, and not by any higher-priority source.
     bool IsUserControlled() const;
 
+    // Returns true if the user can change the Preference value, which is the
+    // case if no higher-priority source than the user store controls the
+    // Preference.
+    bool IsUserModifiable() const;
+
    private:
     friend class PrefService;
 
     Value::ValueType type_;
     std::wstring name_;
     scoped_ptr<Value> default_value_;
 
     // A reference to the pref service's pref_value_store_.
     PrefValueStore* pref_value_store_;
 
@@ skipping 128 matching lines @@
 
   // For the given pref_name, fire any observer of the pref only if |old_value|
   // is different from the current value.  Virtual so it can be mocked for a
   // unit test.
   virtual void FireObserversIfChanged(const wchar_t* pref_name,
                                       const Value* old_value);
 
   bool read_only() const { return pref_value_store_->ReadOnly(); }
 
  protected:
+  // For the given pref_name, fire any observer of the pref.
+  void FireObservers(const wchar_t* pref_name);
+
   // This should only be accessed by subclasses for unit-testing.
   bool PrefIsChanged(const wchar_t* path, const Value* old_value);
 
  private:
   // Add a preference to the PreferenceMap.  If the pref already exists, return
   // false.  This method takes ownership of |pref|.
   void RegisterPreference(Preference* pref);
 
   // Returns a copy of the current pref value.  The caller is responsible for
   // deleting the returned object.
   Value* GetPrefCopy(const wchar_t* pref_name);
 
-  // For the given pref_name, fire any observer of the pref.
-  void FireObservers(const wchar_t* pref_name);
-
   // Load from disk.  Returns a non-zero error code on failure.
   PrefStore::PrefReadError LoadPersistentPrefs();
 
   // Load preferences from storage, attempting to diagnose and handle errors.
   // This should only be called from the constructor.
   void InitFromStorage();
 
   // The value of a Preference can be:
   // managed, user defined, recommended or default.
   // The PrefValueStore manages enforced, user defined and recommended values
@@ skipping 11 matching lines @@
   typedef base::hash_map<std::wstring, NotificationObserverList*>
       PrefObserverMap;
   PrefObserverMap pref_observers_;
 
   friend class ScopedPrefUpdate;
 
   DISALLOW_COPY_AND_ASSIGN(PrefService);
 };
 
 #endif  // CHROME_BROWSER_PREF_SERVICE_H_