Update to current webrtc library

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

webrtc/rtc_base/synchronization/rw_lock_posix.h

@@ -0,0 +1,40 @@
+/*
+ *  Copyright (c) 2011 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.
+ */
+
+#ifndef RTC_BASE_SYNCHRONIZATION_RW_LOCK_POSIX_H_
+#define RTC_BASE_SYNCHRONIZATION_RW_LOCK_POSIX_H_
+
+#include <pthread.h>
+
+#include "rtc_base/synchronization/rw_lock_wrapper.h"
+
+namespace webrtc {
+
+class RWLockPosix : public RWLockWrapper {
+ public:
+  static RWLockPosix* Create();
+  ~RWLockPosix() override;
+
+  void AcquireLockExclusive() override;
+  void ReleaseLockExclusive() override;
+
+  void AcquireLockShared() override;
+  void ReleaseLockShared() override;
+
+ private:
+  RWLockPosix();
+  bool Init();
+
+  pthread_rwlock_t lock_;
+};
+
+}  // namespace webrtc
+
+#endif  // RTC_BASE_SYNCHRONIZATION_RW_LOCK_POSIX_H_