Update to current webrtc library

This is from the upstream library commit id
3326535126e435f1ba647885ce43a8f0f3d317eb, corresponding to Chromium
88.0.4290.1.

webrtc/api/video/hdr_metadata.cc

@@ -0,0 +1,21 @@
+/*
+ *  Copyright (c) 2018 The WebRTC project authors. All Rights Reserved.
+ *
+ *  Use of this source code is governed by a BSD-style license
+ *  that can be found in the LICENSE file in the root of the source
+ *  tree. An additional intellectual property rights grant can be found
+ *  in the file PATENTS.  All contributing project authors may
+ *  be found in the AUTHORS file in the root of the source tree.
+ */
+
+#include "api/video/hdr_metadata.h"
+
+namespace webrtc {
+
+HdrMasteringMetadata::Chromaticity::Chromaticity() = default;
+
+HdrMasteringMetadata::HdrMasteringMetadata() = default;
+
+HdrMetadata::HdrMetadata() = default;
+
+}  // namespace webrtc