Explicitly CHECK arguments in dbus::MessageWriter::AppendString/ObjectPath

dbus/object_path.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 "dbus/object_path.h"
 
+#include "dbus/string_util.h"
+
 namespace dbus {
 
+bool ObjectPath::IsValid() const {
+  return IsValidObjectPath(value_);
+}
+
 bool ObjectPath::operator<(const ObjectPath& that) const {
   return value_ < that.value_;
 }
 
 bool ObjectPath::operator==(const ObjectPath& that) const {
   return value_ == that.value_;
 }
 
 bool ObjectPath::operator!=(const ObjectPath& that) const {
   return value_ != that.value_;
 }
 
 } // namespace dbus