Keep emtpy List/Dictionary pref value with non-empty default.

chrome/browser/prefs/overlay_user_pref_store.cc

 // 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.
 
 #include "chrome/browser/prefs/overlay_user_pref_store.h"
 
 #include "base/memory/scoped_ptr.h"
 #include "base/values.h"
 
 OverlayUserPrefStore::OverlayUserPrefStore(
@@ skipping 83 matching lines @@
 void OverlayUserPrefStore::RemoveValue(const std::string& key) {
   if (!ShallBeStoredInOverlay(key)) {
     underlay_->RemoveValue(GetUnderlayKey(key));
     return;
   }
 
   if (overlay_.RemoveValue(key))
     ReportValueChanged(key);
 }
 
+void OverlayUserPrefStore::MarkNeedsEmptyValue(const std::string& key) {
+  if (!ShallBeStoredInOverlay(key))
+    underlay_->MarkNeedsEmptyValue(key);
+}
+
 bool OverlayUserPrefStore::ReadOnly() const {
   return false;
 }
 
 PersistentPrefStore::PrefReadError OverlayUserPrefStore::GetReadError() const {
   return PersistentPrefStore::PREF_READ_ERROR_NONE;
 }
 
 PersistentPrefStore::PrefReadError OverlayUserPrefStore::ReadPrefs() {
   // We do not read intentionally.
@@ skipping 58 matching lines @@
   NamesMap::const_iterator i =
       overlay_to_underlay_names_map_.find(overlay_key);
   return i != overlay_to_underlay_names_map_.end() ? i->second : overlay_key;
 }
 
 bool OverlayUserPrefStore::ShallBeStoredInOverlay(
     const std::string& key) const {
   return overlay_to_underlay_names_map_.find(key) !=
       overlay_to_underlay_names_map_.end();
 }