Adding PrintTo of ObjectPath for gtest.

dbus/object_path.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.
 
 #ifndef DBUS_OBJECT_PATH_H_
 #define DBUS_OBJECT_PATH_H_
 
+#include <iosfwd>
 #include <string>
 
 #include "dbus/dbus_export.h"
 
 namespace dbus {
 
 // ObjectPath is a type used to distinguish D-Bus object paths from simple
 // strings, especially since normal practice is that these should be only
 // initialized from static constants or obtained from remote objects and no
 // assumptions about their value made.
@@ skipping 21 matching lines @@
 
   // Permit testing for equality, required for mocks to work and useful for
   // observers.
   bool operator==(const ObjectPath&) const;
   bool operator!=(const ObjectPath&) const;
 
  private:
   std::string value_;
 };
 
+// This is required by gtest to print a readable output on test failures.
+CHROME_DBUS_EXPORT void PrintTo(const ObjectPath& path, std::ostream* out);
+
 }  // namespace dbus
 
 #endif  // DBUS_OBJECT_PATH_H_