Introduce incognito preference settings.

chrome/browser/prefs/default_pref_store.cc

+// Copyright (c) 2011 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/default_pref_store.h"
+
+DefaultPrefStore::DefaultPrefStore() {}
+
+DefaultPrefStore::~DefaultPrefStore() {}
+
+void DefaultPrefStore::SetDefaultValue(const std::string& key, Value* value) {
+  CHECK(GetValue(key, NULL) == READ_NO_VALUE);
+  SetValue(key, value);
+}
+
+Value::ValueType DefaultPrefStore::GetType(const std::string& key) const {
+  Value* value;
+  return GetValue(key, &value) == READ_OK ? value->GetType()
+                                          : Value::TYPE_NULL;
+}