metadata_test.cc: add missing copyright header

Change-Id: I11cfbb035475f5726bcf60ca313e1196ad8b9a2f

test/metadata_test.cc

diff --git a/test/metadata_test.cc b/test/metadata_test.cc
index 53aa429..bd8a1dd 100644
--- a/test/metadata_test.cc
+++ b/test/metadata_test.cc
@@ -1,3 +1,14 @@
+/*
+ * Copyright (c) 2019, Alliance for Open Media. All rights reserved
+ *
+ * This source code is subject to the terms of the BSD 2 Clause License and
+ * the Alliance for Open Media Patent License 1.0. If the BSD 2 Clause License
+ * was not distributed with this source code in the LICENSE file, you can
+ * obtain it at www.aomedia.org/license/software. If the Alliance for Open
+ * Media Patent License 1.0 was not distributed with this source code in the
+ * PATENTS file, you can obtain it at www.aomedia.org/license/patent.
+ */
+
 #include "third_party/googletest/src/googletest/include/gtest/gtest.h"
 
 #include "aom/aom_codec.h"