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diff --git a/third_party/libwebrtc/rtc_base/deprecated/recursive_critical_section.h b/third_party/libwebrtc/rtc_base/deprecated/recursive_critical_section.h
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+/*
+ *  Copyright 2004 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_DEPRECATED_RECURSIVE_CRITICAL_SECTION_H_
+#define RTC_BASE_DEPRECATED_RECURSIVE_CRITICAL_SECTION_H_
+
+#include <atomic>
+
+#include "rtc_base/platform_thread_types.h"
+#include "rtc_base/thread_annotations.h"
+
+#if defined(WEBRTC_WIN)
+// clang-format off
+// clang formating would change include order.
+
+// Include winsock2.h before including <windows.h> to maintain consistency with
+// win32.h. To include win32.h directly, it must be broken out into its own
+// build target.
+#include <winsock2.h>
+#include <windows.h>
+#include <sal.h>  // must come after windows headers.
+// clang-format on
+#endif  // defined(WEBRTC_WIN)
+
+#if defined(WEBRTC_POSIX)
+#include <pthread.h>
+#endif
+
+// See notes in the 'Performance' unit test for the effects of this flag.
+#define RTC_USE_NATIVE_MUTEX_ON_MAC 1
+
+#if defined(WEBRTC_MAC) && !RTC_USE_NATIVE_MUTEX_ON_MAC
+#include <dispatch/dispatch.h>
+#endif
+
+namespace rtc {
+
+// NOTE: This class is deprecated. Please use webrtc::Mutex instead!
+// Search using https://www.google.com/?q=recursive+lock+considered+harmful
+// to find the reasons.
+//
+// Locking methods (Enter, TryEnter, Leave)are const to permit protecting
+// members inside a const context without requiring mutable
+// RecursiveCriticalSections everywhere. RecursiveCriticalSection is
+// reentrant lock.
+class RTC_LOCKABLE RecursiveCriticalSection {
+ public:
+  RecursiveCriticalSection();
+  ~RecursiveCriticalSection();
+
+  void Enter() const RTC_EXCLUSIVE_LOCK_FUNCTION();
+  bool TryEnter() const RTC_EXCLUSIVE_TRYLOCK_FUNCTION(true);
+  void Leave() const RTC_UNLOCK_FUNCTION();
+
+ private:
+  // Use only for RTC_DCHECKing.
+  bool CurrentThreadIsOwner() const;
+
+#if defined(WEBRTC_WIN)
+  mutable CRITICAL_SECTION crit_;
+#elif defined(WEBRTC_POSIX)
+#if defined(WEBRTC_MAC) && !RTC_USE_NATIVE_MUTEX_ON_MAC
+  // Number of times the lock has been locked + number of threads waiting.
+  // TODO(tommi): We could use this number and subtract the recursion count
+  // to find places where we have multiple threads contending on the same lock.
+  mutable std::atomic<int> lock_queue_;
+  // `recursion_` represents the recursion count + 1 for the thread that owns
+  // the lock. Only modified by the thread that owns the lock.
+  mutable int recursion_;
+  // Used to signal a single waiting thread when the lock becomes available.
+  mutable dispatch_semaphore_t semaphore_;
+  // The thread that currently holds the lock. Required to handle recursion.
+  mutable PlatformThreadRef owning_thread_;
+#else
+  mutable pthread_mutex_t mutex_;
+#endif
+  mutable PlatformThreadRef thread_;  // Only used by RTC_DCHECKs.
+  mutable int recursion_count_;       // Only used by RTC_DCHECKs.
+#else  // !defined(WEBRTC_WIN) && !defined(WEBRTC_POSIX)
+#error Unsupported platform.
+#endif
+};
+
+// CritScope, for serializing execution through a scope.
+class RTC_SCOPED_LOCKABLE CritScope {
+ public:
+  explicit CritScope(const RecursiveCriticalSection* cs)
+      RTC_EXCLUSIVE_LOCK_FUNCTION(cs);
+  ~CritScope() RTC_UNLOCK_FUNCTION();
+
+  CritScope(const CritScope&) = delete;
+  CritScope& operator=(const CritScope&) = delete;
+
+ private:
+  const RecursiveCriticalSection* const cs_;
+};
+
+}  // namespace rtc
+
+#endif  // RTC_BASE_DEPRECATED_RECURSIVE_CRITICAL_SECTION_H_