Adjust preference sync code to only sync user modifiable preferences.

chrome/browser/pref_value_store.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.
 
 #ifndef CHROME_BROWSER_PREF_VALUE_STORE_H_
 #define CHROME_BROWSER_PREF_VALUE_STORE_H_
 
 #include "base/basictypes.h"
 #include "base/file_path.h"
 #include "base/string16.h"
@@ skipping 78 matching lines @@
   bool PrefValueInManagedStore(const wchar_t* name);
   bool PrefValueInExtensionStore(const wchar_t* name);
   bool PrefValueInUserStore(const wchar_t* name);
 
   // These methods return true if a preference with the given name is actually
   // being controlled by the indicated pref store and not being overridden by
   // a higher-priority source.
   bool PrefValueFromExtensionStore(const wchar_t* name);
   bool PrefValueFromUserStore(const wchar_t* name);
 
+  // Check whether a Preference value is modifiable by the user, i.e. whether
+  // there is no higher-priority source controlling it.
+  bool PrefValueUserModifiable(const wchar_t* name);
+
  private:
   // PrefStores must be listed here in order from highest to lowest priority.
   enum PrefStoreType {
+    // Not associated with an actual PrefStore but used as invalid marker, e.g.
+    // as return value.
+    INVALID = -1,
     MANAGED = 0,
     EXTENSION,
     COMMAND_LINE,
     USER,
     RECOMMENDED,
     PREF_STORE_TYPE_MAX = RECOMMENDED
   };
 
   scoped_ptr<PrefStore> pref_stores_[PREF_STORE_TYPE_MAX + 1];
 
   bool PrefValueInStore(const wchar_t* name, PrefStoreType type);
 
-  bool PrefValueFromStore(const wchar_t* name, PrefStoreType type);
+  // Returns the pref store type identifying the source that controls the
+  // Preference identified by |name|. If none of the sources has a value,
+  // INVALID is returned.
+  PrefStoreType ControllingPrefStoreForPref(const wchar_t* name);
 
   DISALLOW_COPY_AND_ASSIGN(PrefValueStore);
 };
 
 #endif  // CHROME_BROWSER_PREF_VALUE_STORE_H_