Introduce a temporary workaround to ensure tracked preferences set to empty list/dict are not confu…

base/prefs/pref_service.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.
 
 // This provides a way to access the application's current preferences.
 
 // Chromium settings and storage represent user-selected preferences and
 // information and MUST not be extracted, overwritten or modified except
 // through Chromium defined APIs.
 
@@ skipping 203 matching lines @@
   // Changes the default value for a preference. Takes ownership of |value|.
   //
   // Will cause a pref change notification to be fired if this causes
   // the effective value to change.
   void SetDefaultPrefValue(const char* path, base::Value* value);
 
   // Returns the default value of the given preference. |path| must point to a
   // registered preference. In that case, will never return NULL.
   const base::Value* GetDefaultPrefValue(const char* path) const;
 
+  // Deprecated. Do not add calls to this method.
+  // Marks that the user store should not prune out empty values for |key| when
+  // writting to disk.
+  // TODO(gab): Enforce this at a lower level for all values and remove this
+  // method.
+  void MarkUserStoreNeedsEmptyValue(const std::string& key) const;
+
   // Returns true if a value has been set for the specified path.
   // NOTE: this is NOT the same as FindPreference. In particular
   // FindPreference returns whether RegisterXXX has been invoked, where as
   // this checks if a value exists for the path.
   bool HasPrefPath(const char* path) const;
 
   // Returns a dictionary with effective preference values. The ownership
   // is passed to the caller.
   scoped_ptr<base::DictionaryValue> GetPreferenceValues() const;
 
@@ skipping 117 matching lines @@
 
   // Local cache of registered Preference objects. The pref_registry_
   // is authoritative with respect to what the types and default values
   // of registered preferences are.
   mutable PreferenceMap prefs_map_;
 
   DISALLOW_COPY_AND_ASSIGN(PrefService);
 };
 
 #endif  // BASE_PREFS_PREF_SERVICE_H_