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

chrome/browser/prefs/pref_service.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/pref_service.h"
 
 #include <algorithm>
 #include <string>
 
 #include "base/bind.h"
@@ skipping 709 matching lines @@
 
   if (FindPreference(path)) {
     NOTREACHED() << "Tried to register duplicate pref " << path;
     return;
   }
 
   base::Value::Type orig_type = default_value->GetType();
   DCHECK(orig_type != Value::TYPE_NULL && orig_type != Value::TYPE_BINARY) <<
          "invalid preference type: " << orig_type;
 
+  // For ListValue and DictionaryValue with non empty default, empty value
+  // for |path| needs to be persisted in |user_pref_store_|. So that
+  // non empty default is not used when user sets an empty ListValue or
+  // DictionaryValue.
+  bool needs_empty_value = false;
+  if (orig_type == base::Value::TYPE_LIST) {
+    const base::ListValue* list = NULL;
+    if (default_value->GetAsList(&list) && !list->empty())
+      needs_empty_value = true;
+  } else if (orig_type == base::Value::TYPE_DICTIONARY) {
+    const base::DictionaryValue* dict = NULL;
+    if (default_value->GetAsDictionary(&dict) && !dict->empty())
+      needs_empty_value = true;
+  }
+  if (needs_empty_value)
+    user_pref_store_->MarkNeedsEmptyValue(path);
+
   // Hand off ownership.
   default_store_->SetDefaultValue(path, scoped_value.release());
 
   // Register with sync if necessary.
   if (sync_status == SYNCABLE_PREF && pref_sync_associator_.get())
     pref_sync_associator_->RegisterPref(path);
 }
 
 void PrefService::UnregisterPreference(const char* path) {
   DCHECK(CalledOnValidThread());
@@ skipping 198 matching lines @@
   return pref_value_store()->PrefValueFromDefaultStore(name_.c_str());
 }
 
 bool PrefService::Preference::IsUserModifiable() const {
   return pref_value_store()->PrefValueUserModifiable(name_.c_str());
 }
 
 bool PrefService::Preference::IsExtensionModifiable() const {
   return pref_value_store()->PrefValueExtensionModifiable(name_.c_str());
 }