Adding PrintTo of ObjectPath for gtest.

dbus/object_path.cc

Index: dbus/object_path.cc
diff --git a/dbus/object_path.cc b/dbus/object_path.cc
index 1200a9bace623f3d5d815124b54c3ffab227dada..8606b6bbca1962b884eefdc077ebd1ef73f4fb35 100644
--- a/dbus/object_path.cc
+++ b/dbus/object_path.cc
@@ -4,6 +4,8 @@
 
 #include "dbus/object_path.h"
 
+#include <ostream>
+
 #include "dbus/string_util.h"
 
 namespace dbus {
@@ -24,4 +26,8 @@ bool ObjectPath::operator!=(const ObjectPath& that) const {
   return value_ != that.value_;
 }
 
+void PrintTo(const ObjectPath& path, std::ostream* out) {
+  *out << path.value();
+}
+
 } // namespace dbus