Update to current webrtc library

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

webrtc/rtc_base/ref_counter.h

@@ -0,0 +1,75 @@
+/*
+ *  Copyright 2017 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_REF_COUNTER_H_
+#define RTC_BASE_REF_COUNTER_H_
+
+#include <atomic>
+
+#include "rtc_base/ref_count.h"
+
+namespace webrtc {
+namespace webrtc_impl {
+
+class RefCounter {
+ public:
+  explicit RefCounter(int ref_count) : ref_count_(ref_count) {}
+  RefCounter() = delete;
+
+  void IncRef() {
+    // Relaxed memory order: The current thread is allowed to act on the
+    // resource protected by the reference counter both before and after the
+    // atomic op, so this function doesn't prevent memory access reordering.
+    ref_count_.fetch_add(1, std::memory_order_relaxed);
+  }
+
+  // Returns kDroppedLastRef if this call dropped the last reference; the caller
+  // should therefore free the resource protected by the reference counter.
+  // Otherwise, returns kOtherRefsRemained (note that in case of multithreading,
+  // some other caller may have dropped the last reference by the time this call
+  // returns; all we know is that we didn't do it).
+  rtc::RefCountReleaseStatus DecRef() {
+    // Use release-acquire barrier to ensure all actions on the protected
+    // resource are finished before the resource can be freed.
+    // When ref_count_after_subtract > 0, this function require
+    // std::memory_order_release part of the barrier.
+    // When ref_count_after_subtract == 0, this function require
+    // std::memory_order_acquire part of the barrier.
+    // In addition std::memory_order_release is used for synchronization with
+    // the HasOneRef function to make sure all actions on the protected resource
+    // are finished before the resource is assumed to have exclusive access.
+    int ref_count_after_subtract =
+        ref_count_.fetch_sub(1, std::memory_order_acq_rel) - 1;
+    return ref_count_after_subtract == 0
+               ? rtc::RefCountReleaseStatus::kDroppedLastRef
+               : rtc::RefCountReleaseStatus::kOtherRefsRemained;
+  }
+
+  // Return whether the reference count is one. If the reference count is used
+  // in the conventional way, a reference count of 1 implies that the current
+  // thread owns the reference and no other thread shares it. This call performs
+  // the test for a reference count of one, and performs the memory barrier
+  // needed for the owning thread to act on the resource protected by the
+  // reference counter, knowing that it has exclusive access.
+  bool HasOneRef() const {
+    // To ensure resource protected by the reference counter has exclusive
+    // access, all changes to the resource before it was released by other
+    // threads must be visible by current thread. That is provided by release
+    // (in DecRef) and acquire (in this function) ordering.
+    return ref_count_.load(std::memory_order_acquire) == 1;
+  }
+
+ private:
+  std::atomic<int> ref_count_;
+};
+
+}  // namespace webrtc_impl
+}  // namespace webrtc
+
+#endif  // RTC_BASE_REF_COUNTER_H_