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diff --git a/third_party/libwebrtc/rtc_base/strong_alias_unittest.cc b/third_party/libwebrtc/rtc_base/strong_alias_unittest.cc
new file mode 100644
index 0000000000..a87bc4de37
--- /dev/null
+++ b/third_party/libwebrtc/rtc_base/strong_alias_unittest.cc
@@ -0,0 +1,362 @@
+/*
+ *  Copyright 2019 The Chromium Authors. All rights reserved.
+ *  Copyright (c) 2021 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 "rtc_base/strong_alias.h"
+
+#include <cstdint>
+#include <map>
+#include <memory>
+#include <string>
+#include <type_traits>
+#include <utility>
+
+#include "rtc_base/containers/flat_map.h"
+#include "rtc_base/gunit.h"
+#include "test/gmock.h"
+
+// This is a copy of
+// https://source.chromium.org/chromium/chromium/src/+/main:base/types/strong_alias_unittest.cc
+// but adapted to use WebRTC's includes, remove unit tests that test the ostream
+// operator (it's removed in this port) and other adaptations to pass lint.
+
+namespace webrtc {
+namespace {
+
+// For test correctnenss, it's important that these getters return lexically
+// incrementing values as `index` grows.
+template <typename T>
+T GetExampleValue(int index);
+
+template <>
+int GetExampleValue<int>(int index) {
+  return 5 + index;
+}
+template <>
+uint64_t GetExampleValue<uint64_t>(int index) {
+  return 500U + index;
+}
+
+template <>
+std::string GetExampleValue<std::string>(int index) {
+  return std::string('a', index);
+}
+
+}  // namespace
+
+template <typename T>
+class StrongAliasTest : public ::testing::Test {};
+
+using TestedTypes = ::testing::Types<int, uint64_t, std::string>;
+TYPED_TEST_SUITE(StrongAliasTest, TestedTypes);
+
+TYPED_TEST(StrongAliasTest, ValueAccessesUnderlyingValue) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+
+  // Const value getter.
+  const FooAlias const_alias(GetExampleValue<TypeParam>(1));
+  EXPECT_EQ(GetExampleValue<TypeParam>(1), const_alias.value());
+  static_assert(std::is_const<typename std::remove_reference<decltype(
+                    const_alias.value())>::type>::value,
+                "Reference returned by const value getter should be const.");
+}
+
+TYPED_TEST(StrongAliasTest, ExplicitConversionToUnderlyingValue) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+
+  const FooAlias const_alias(GetExampleValue<TypeParam>(1));
+  EXPECT_EQ(GetExampleValue<TypeParam>(1), static_cast<TypeParam>(const_alias));
+}
+
+TYPED_TEST(StrongAliasTest, CanBeCopyConstructed) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  FooAlias alias(GetExampleValue<TypeParam>(0));
+  FooAlias copy_constructed = alias;
+  EXPECT_EQ(copy_constructed, alias);
+
+  FooAlias copy_assigned;
+  copy_assigned = alias;
+  EXPECT_EQ(copy_assigned, alias);
+}
+
+TYPED_TEST(StrongAliasTest, CanBeMoveConstructed) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  FooAlias alias(GetExampleValue<TypeParam>(0));
+  FooAlias move_constructed = std::move(alias);
+  EXPECT_EQ(move_constructed, FooAlias(GetExampleValue<TypeParam>(0)));
+
+  FooAlias alias2(GetExampleValue<TypeParam>(2));
+  FooAlias move_assigned;
+  move_assigned = std::move(alias2);
+  EXPECT_EQ(move_assigned, FooAlias(GetExampleValue<TypeParam>(2)));
+
+  // Check that FooAlias is nothrow move constructible. This matters for
+  // performance when used in std::vectors.
+  static_assert(std::is_nothrow_move_constructible<FooAlias>::value,
+                "Error: Alias is not nothow move constructible");
+}
+
+TYPED_TEST(StrongAliasTest, CanBeConstructedFromMoveOnlyType) {
+  // Note, using a move-only unique_ptr to T:
+  using FooAlias = StrongAlias<class FooTag, std::unique_ptr<TypeParam>>;
+
+  FooAlias a(std::make_unique<TypeParam>(GetExampleValue<TypeParam>(0)));
+  EXPECT_EQ(*a.value(), GetExampleValue<TypeParam>(0));
+
+  auto bare_value = std::make_unique<TypeParam>(GetExampleValue<TypeParam>(1));
+  FooAlias b(std::move(bare_value));
+  EXPECT_EQ(*b.value(), GetExampleValue<TypeParam>(1));
+}
+
+TYPED_TEST(StrongAliasTest, MutableOperatorArrow) {
+  // Note, using a move-only unique_ptr to T:
+  using Ptr = std::unique_ptr<TypeParam>;
+  using FooAlias = StrongAlias<class FooTag, Ptr>;
+
+  FooAlias a(std::make_unique<TypeParam>());
+  EXPECT_TRUE(a.value());
+
+  // Check that `a` can be modified through the use of operator->.
+  a->reset();
+
+  EXPECT_FALSE(a.value());
+}
+
+TYPED_TEST(StrongAliasTest, MutableOperatorStar) {
+  // Note, using a move-only unique_ptr to T:
+  using Ptr = std::unique_ptr<TypeParam>;
+  using FooAlias = StrongAlias<class FooTag, Ptr>;
+
+  FooAlias a(std::make_unique<TypeParam>());
+  FooAlias b(std::make_unique<TypeParam>());
+  EXPECT_TRUE(*a);
+  EXPECT_TRUE(*b);
+
+  // Check that both the mutable l-value and r-value overloads work and we can
+  // move out of the aliases.
+  { Ptr ignore(*std::move(a)); }
+  { Ptr ignore(std::move(*b)); }
+
+  EXPECT_FALSE(a.value());
+  EXPECT_FALSE(b.value());
+}
+
+TYPED_TEST(StrongAliasTest, MutableValue) {
+  // Note, using a move-only unique_ptr to T:
+  using Ptr = std::unique_ptr<TypeParam>;
+  using FooAlias = StrongAlias<class FooTag, Ptr>;
+
+  FooAlias a(std::make_unique<TypeParam>());
+  FooAlias b(std::make_unique<TypeParam>());
+  EXPECT_TRUE(a.value());
+  EXPECT_TRUE(b.value());
+
+  // Check that both the mutable l-value and r-value overloads work and we can
+  // move out of the aliases.
+  { Ptr ignore(std::move(a).value()); }
+  { Ptr ignore(std::move(b.value())); }
+
+  EXPECT_FALSE(a.value());
+  EXPECT_FALSE(b.value());
+}
+
+TYPED_TEST(StrongAliasTest, SizeSameAsUnderlyingType) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  static_assert(sizeof(FooAlias) == sizeof(TypeParam),
+                "StrongAlias should be as large as the underlying type.");
+}
+
+TYPED_TEST(StrongAliasTest, IsDefaultConstructible) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  static_assert(std::is_default_constructible<FooAlias>::value,
+                "Should be possible to default-construct a StrongAlias.");
+  static_assert(
+      std::is_trivially_default_constructible<FooAlias>::value ==
+          std::is_trivially_default_constructible<TypeParam>::value,
+      "Should be possible to trivially default-construct a StrongAlias iff the "
+      "underlying type is trivially default constructible.");
+}
+
+TEST(StrongAliasTest, TrivialTypeAliasIsStandardLayout) {
+  using FooAlias = StrongAlias<class FooTag, int>;
+  static_assert(std::is_standard_layout<FooAlias>::value,
+                "int-based alias should have standard layout. ");
+  static_assert(std::is_trivially_copyable<FooAlias>::value,
+                "int-based alias should be trivially copyable. ");
+}
+
+TYPED_TEST(StrongAliasTest, CannotBeCreatedFromDifferentAlias) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  using BarAlias = StrongAlias<class BarTag, TypeParam>;
+  static_assert(!std::is_constructible<FooAlias, BarAlias>::value,
+                "Should be impossible to construct FooAlias from a BarAlias.");
+  static_assert(!std::is_convertible<BarAlias, FooAlias>::value,
+                "Should be impossible to convert a BarAlias into FooAlias.");
+}
+
+TYPED_TEST(StrongAliasTest, CannotBeImplicitlyConverterToUnderlyingValue) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  static_assert(!std::is_convertible<FooAlias, TypeParam>::value,
+                "Should be impossible to implicitly convert a StrongAlias into "
+                "an underlying type.");
+}
+
+TYPED_TEST(StrongAliasTest, ComparesEqualToSameValue) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  // Comparison to self:
+  const FooAlias a = FooAlias(GetExampleValue<TypeParam>(0));
+  EXPECT_EQ(a, a);
+  EXPECT_FALSE(a != a);
+  EXPECT_TRUE(a >= a);
+  EXPECT_TRUE(a <= a);
+  EXPECT_FALSE(a > a);
+  EXPECT_FALSE(a < a);
+  // Comparison to other equal object:
+  const FooAlias b = FooAlias(GetExampleValue<TypeParam>(0));
+  EXPECT_EQ(a, b);
+  EXPECT_FALSE(a != b);
+  EXPECT_TRUE(a >= b);
+  EXPECT_TRUE(a <= b);
+  EXPECT_FALSE(a > b);
+  EXPECT_FALSE(a < b);
+}
+
+TYPED_TEST(StrongAliasTest, ComparesCorrectlyToDifferentValue) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  const FooAlias a = FooAlias(GetExampleValue<TypeParam>(0));
+  const FooAlias b = FooAlias(GetExampleValue<TypeParam>(1));
+  EXPECT_NE(a, b);
+  EXPECT_FALSE(a == b);
+  EXPECT_TRUE(b >= a);
+  EXPECT_TRUE(a <= b);
+  EXPECT_TRUE(b > a);
+  EXPECT_TRUE(a < b);
+}
+
+TEST(StrongAliasTest, CanBeDerivedFrom) {
+  // Aliases can be enriched by custom operations or validations if needed.
+  // Ideally, one could go from a 'using' declaration to a derived class to add
+  // those methods without the need to change any other code.
+  class CountryCode : public StrongAlias<CountryCode, std::string> {
+   public:
+    explicit CountryCode(const std::string& value)
+        : StrongAlias<CountryCode, std::string>::StrongAlias(value) {
+      if (value_.length() != 2) {
+        // Country code invalid!
+        value_.clear();  // is_null() will return true.
+      }
+    }
+
+    bool is_null() const { return value_.empty(); }
+  };
+
+  CountryCode valid("US");
+  EXPECT_FALSE(valid.is_null());
+
+  CountryCode invalid("United States");
+  EXPECT_TRUE(invalid.is_null());
+}
+
+TEST(StrongAliasTest, CanWrapComplexStructures) {
+  // A pair of strings implements odering and can, in principle, be used as
+  // a base of StrongAlias.
+  using PairOfStrings = std::pair<std::string, std::string>;
+  using ComplexAlias = StrongAlias<class FooTag, PairOfStrings>;
+
+  ComplexAlias a1{std::make_pair("aaa", "bbb")};
+  ComplexAlias a2{std::make_pair("ccc", "ddd")};
+  EXPECT_TRUE(a1 < a2);
+
+  EXPECT_TRUE(a1.value() == PairOfStrings("aaa", "bbb"));
+
+  // Note a caveat, an std::pair doesn't have an overload of operator<<, and it
+  // cannot be easily added since ADL rules would require it to be in the std
+  // namespace. So we can't print ComplexAlias.
+}
+
+TYPED_TEST(StrongAliasTest, CanBeKeysInFlatMap) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  webrtc::flat_map<FooAlias, std::string> map;
+
+  FooAlias k1(GetExampleValue<TypeParam>(0));
+  FooAlias k2(GetExampleValue<TypeParam>(1));
+
+  map[k1] = "value1";
+  map[k2] = "value2";
+
+  EXPECT_EQ(map[k1], "value1");
+  EXPECT_EQ(map[k2], "value2");
+}
+
+TYPED_TEST(StrongAliasTest, CanBeKeysInStdMap) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  std::map<FooAlias, std::string> map;
+
+  FooAlias k1(GetExampleValue<TypeParam>(0));
+  FooAlias k2(GetExampleValue<TypeParam>(1));
+
+  map[k1] = "value1";
+  map[k2] = "value2";
+
+  EXPECT_EQ(map[k1], "value1");
+  EXPECT_EQ(map[k2], "value2");
+}
+
+TYPED_TEST(StrongAliasTest, CanDifferentiateOverloads) {
+  using FooAlias = StrongAlias<class FooTag, TypeParam>;
+  using BarAlias = StrongAlias<class BarTag, TypeParam>;
+  class Scope {
+   public:
+    static std::string Overload(FooAlias) { return "FooAlias"; }
+    static std::string Overload(BarAlias) { return "BarAlias"; }
+  };
+  EXPECT_EQ("FooAlias", Scope::Overload(FooAlias()));
+  EXPECT_EQ("BarAlias", Scope::Overload(BarAlias()));
+}
+
+TEST(StrongAliasTest, EnsureConstexpr) {
+  using FooAlias = StrongAlias<class FooTag, int>;
+
+  // Check constructors.
+  static constexpr FooAlias kZero{};
+  static constexpr FooAlias kOne(1);
+
+  // Check operator*.
+  static_assert(*kZero == 0, "");
+  static_assert(*kOne == 1, "");
+
+  // Check value().
+  static_assert(kZero.value() == 0, "");
+  static_assert(kOne.value() == 1, "");
+
+  // Check explicit conversions to underlying type.
+  static_assert(static_cast<int>(kZero) == 0, "");
+  static_assert(static_cast<int>(kOne) == 1, "");
+
+  // Check comparison operations.
+  static_assert(kZero == kZero, "");
+  static_assert(kZero != kOne, "");
+  static_assert(kZero < kOne, "");
+  static_assert(kZero <= kOne, "");
+  static_assert(kOne > kZero, "");
+  static_assert(kOne >= kZero, "");
+}
+
+TEST(StrongAliasTest, BooleansAreEvaluatedAsBooleans) {
+  using BoolAlias = StrongAlias<class BoolTag, bool>;
+
+  BoolAlias happy(true);
+  BoolAlias sad(false);
+
+  EXPECT_TRUE(happy);
+  EXPECT_FALSE(sad);
+  EXPECT_TRUE(*happy);
+  EXPECT_FALSE(*sad);
+}
+}  // namespace webrtc