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diff --git a/third_party/libwebrtc/system_wrappers/source/field_trial.cc b/third_party/libwebrtc/system_wrappers/source/field_trial.cc
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+++ b/third_party/libwebrtc/system_wrappers/source/field_trial.cc
@@ -0,0 +1,181 @@
+// Copyright (c) 2014 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 "system_wrappers/include/field_trial.h"
+
+#include <stddef.h>
+
+#include <map>
+#include <string>
+#include <utility>
+
+#include "absl/algorithm/container.h"
+#include "absl/strings/string_view.h"
+#include "experiments/registered_field_trials.h"
+#include "rtc_base/checks.h"
+#include "rtc_base/containers/flat_set.h"
+#include "rtc_base/logging.h"
+#include "rtc_base/string_encode.h"
+
+// Simple field trial implementation, which allows client to
+// specify desired flags in InitFieldTrialsFromString.
+namespace webrtc {
+namespace field_trial {
+
+static const char* trials_init_string = NULL;
+
+namespace {
+
+constexpr char kPersistentStringSeparator = '/';
+
+flat_set<std::string>& TestKeys() {
+  static auto* test_keys = new flat_set<std::string>();
+  return *test_keys;
+}
+
+// Validates the given field trial string.
+//  E.g.:
+//    "WebRTC-experimentFoo/Enabled/WebRTC-experimentBar/Enabled100kbps/"
+//    Assigns the process to group "Enabled" on WebRTCExperimentFoo trial
+//    and to group "Enabled100kbps" on WebRTCExperimentBar.
+//
+//  E.g. invalid config:
+//    "WebRTC-experiment1/Enabled"  (note missing / separator at the end).
+bool FieldTrialsStringIsValidInternal(const absl::string_view trials) {
+  if (trials.empty())
+    return true;
+
+  size_t next_item = 0;
+  std::map<absl::string_view, absl::string_view> field_trials;
+  while (next_item < trials.length()) {
+    size_t name_end = trials.find(kPersistentStringSeparator, next_item);
+    if (name_end == trials.npos || next_item == name_end)
+      return false;
+    size_t group_name_end =
+        trials.find(kPersistentStringSeparator, name_end + 1);
+    if (group_name_end == trials.npos || name_end + 1 == group_name_end)
+      return false;
+    absl::string_view name = trials.substr(next_item, name_end - next_item);
+    absl::string_view group_name =
+        trials.substr(name_end + 1, group_name_end - name_end - 1);
+
+    next_item = group_name_end + 1;
+
+    // Fail if duplicate with different group name.
+    if (field_trials.find(name) != field_trials.end() &&
+        field_trials.find(name)->second != group_name) {
+      return false;
+    }
+
+    field_trials[name] = group_name;
+  }
+
+  return true;
+}
+
+}  // namespace
+
+bool FieldTrialsStringIsValid(absl::string_view trials_string) {
+  return FieldTrialsStringIsValidInternal(trials_string);
+}
+
+void InsertOrReplaceFieldTrialStringsInMap(
+    std::map<std::string, std::string>* fieldtrial_map,
+    const absl::string_view trials_string) {
+  if (FieldTrialsStringIsValidInternal(trials_string)) {
+    std::vector<absl::string_view> tokens = rtc::split(trials_string, '/');
+    // Skip last token which is empty due to trailing '/'.
+    for (size_t idx = 0; idx < tokens.size() - 1; idx += 2) {
+      (*fieldtrial_map)[std::string(tokens[idx])] =
+          std::string(tokens[idx + 1]);
+    }
+  } else {
+    RTC_DCHECK_NOTREACHED() << "Invalid field trials string:" << trials_string;
+  }
+}
+
+std::string MergeFieldTrialsStrings(absl::string_view first,
+                                    absl::string_view second) {
+  std::map<std::string, std::string> fieldtrial_map;
+  InsertOrReplaceFieldTrialStringsInMap(&fieldtrial_map, first);
+  InsertOrReplaceFieldTrialStringsInMap(&fieldtrial_map, second);
+
+  // Merge into fieldtrial string.
+  std::string merged = "";
+  for (auto const& fieldtrial : fieldtrial_map) {
+    merged += fieldtrial.first + '/' + fieldtrial.second + '/';
+  }
+  return merged;
+}
+
+#ifndef WEBRTC_EXCLUDE_FIELD_TRIAL_DEFAULT
+std::string FindFullName(absl::string_view name) {
+#if WEBRTC_STRICT_FIELD_TRIALS
+  RTC_DCHECK(absl::c_linear_search(kRegisteredFieldTrials, name) ||
+             TestKeys().contains(name))
+      << name << " is not registered.";
+#endif
+
+  if (trials_init_string == NULL)
+    return std::string();
+
+  absl::string_view trials_string(trials_init_string);
+  if (trials_string.empty())
+    return std::string();
+
+  size_t next_item = 0;
+  while (next_item < trials_string.length()) {
+    // Find next name/value pair in field trial configuration string.
+    size_t field_name_end =
+        trials_string.find(kPersistentStringSeparator, next_item);
+    if (field_name_end == trials_string.npos || field_name_end == next_item)
+      break;
+    size_t field_value_end =
+        trials_string.find(kPersistentStringSeparator, field_name_end + 1);
+    if (field_value_end == trials_string.npos ||
+        field_value_end == field_name_end + 1)
+      break;
+    absl::string_view field_name =
+        trials_string.substr(next_item, field_name_end - next_item);
+    absl::string_view field_value = trials_string.substr(
+        field_name_end + 1, field_value_end - field_name_end - 1);
+    next_item = field_value_end + 1;
+
+    if (name == field_name)
+      return std::string(field_value);
+  }
+  return std::string();
+}
+#endif  // WEBRTC_EXCLUDE_FIELD_TRIAL_DEFAULT
+
+// Optionally initialize field trial from a string.
+void InitFieldTrialsFromString(const char* trials_string) {
+  RTC_LOG(LS_INFO) << "Setting field trial string:" << trials_string;
+  if (trials_string) {
+    RTC_DCHECK(FieldTrialsStringIsValidInternal(trials_string))
+        << "Invalid field trials string:" << trials_string;
+  };
+  trials_init_string = trials_string;
+}
+
+const char* GetFieldTrialString() {
+  return trials_init_string;
+}
+
+FieldTrialsAllowedInScopeForTesting::FieldTrialsAllowedInScopeForTesting(
+    flat_set<std::string> keys) {
+  TestKeys() = std::move(keys);
+}
+
+FieldTrialsAllowedInScopeForTesting::~FieldTrialsAllowedInScopeForTesting() {
+  TestKeys().clear();
+}
+
+}  // namespace field_trial
+}  // namespace webrtc