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diff --git a/third_party/libwebrtc/rtc_base/synchronization/mutex.h b/third_party/libwebrtc/rtc_base/synchronization/mutex.h
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+++ b/third_party/libwebrtc/rtc_base/synchronization/mutex.h
@@ -0,0 +1,77 @@
+/*
+ *  Copyright 2020 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_MUTEX_H_
+#define RTC_BASE_SYNCHRONIZATION_MUTEX_H_
+
+#include <atomic>
+
+#include "absl/base/attributes.h"
+#include "absl/base/const_init.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/thread_annotations.h"
+
+#if defined(WEBRTC_ABSL_MUTEX)
+#include "rtc_base/synchronization/mutex_abseil.h"  // nogncheck
+#elif defined(WEBRTC_WIN)
+#include "rtc_base/synchronization/mutex_critical_section.h"
+#elif defined(WEBRTC_POSIX)
+#include "rtc_base/synchronization/mutex_pthread.h"
+#else
+#error Unsupported platform.
+#endif
+
+namespace webrtc {
+
+// The Mutex guarantees exclusive access and aims to follow Abseil semantics
+// (i.e. non-reentrant etc).
+class RTC_LOCKABLE Mutex final {
+ public:
+  Mutex() = default;
+  Mutex(const Mutex&) = delete;
+  Mutex& operator=(const Mutex&) = delete;
+
+  void Lock() RTC_EXCLUSIVE_LOCK_FUNCTION() {
+    impl_.Lock();
+  }
+  ABSL_MUST_USE_RESULT bool TryLock() RTC_EXCLUSIVE_TRYLOCK_FUNCTION(true) {
+    return impl_.TryLock();
+  }
+  // Return immediately if this thread holds the mutex, or RTC_DCHECK_IS_ON==0.
+  // Otherwise, may report an error (typically by crashing with a diagnostic),
+  // or may return immediately.
+  void AssertHeld() const RTC_ASSERT_EXCLUSIVE_LOCK() { impl_.AssertHeld(); }
+  void Unlock() RTC_UNLOCK_FUNCTION() {
+    impl_.Unlock();
+  }
+
+ private:
+  MutexImpl impl_;
+};
+
+// MutexLock, for serializing execution through a scope.
+class RTC_SCOPED_LOCKABLE MutexLock final {
+ public:
+  MutexLock(const MutexLock&) = delete;
+  MutexLock& operator=(const MutexLock&) = delete;
+
+  explicit MutexLock(Mutex* mutex) RTC_EXCLUSIVE_LOCK_FUNCTION(mutex)
+      : mutex_(mutex) {
+    mutex->Lock();
+  }
+  ~MutexLock() RTC_UNLOCK_FUNCTION() { mutex_->Unlock(); }
+
+ private:
+  Mutex* mutex_;
+};
+
+}  // namespace webrtc
+
+#endif  // RTC_BASE_SYNCHRONIZATION_MUTEX_H_