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diff --git a/third_party/libwebrtc/api/field_trials_registry.h b/third_party/libwebrtc/api/field_trials_registry.h
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+++ b/third_party/libwebrtc/api/field_trials_registry.h
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+/*
+ *  Copyright 2022 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 API_FIELD_TRIALS_REGISTRY_H_
+#define API_FIELD_TRIALS_REGISTRY_H_
+
+#include <string>
+#include <utility>
+
+#include "absl/strings/string_view.h"
+#include "api/field_trials_view.h"
+#include "rtc_base/containers/flat_set.h"
+#include "rtc_base/system/rtc_export.h"
+
+namespace webrtc {
+
+// Abstract base class for a field trial registry that verifies that any looked
+// up key has been pre-registered in accordance with `g3doc/field-trials.md`.
+class RTC_EXPORT FieldTrialsRegistry : public FieldTrialsView {
+ public:
+  FieldTrialsRegistry() = default;
+
+  FieldTrialsRegistry(const FieldTrialsRegistry&) = default;
+  FieldTrialsRegistry& operator=(const FieldTrialsRegistry&) = default;
+
+  ~FieldTrialsRegistry() override = default;
+
+  // Verifies that `key` is a registered field trial and then returns the
+  // configured value for `key` or an empty string if the field trial isn't
+  // configured.
+  std::string Lookup(absl::string_view key) const override;
+
+  // Register additional `keys` for testing. This should only be used for
+  // imaginary keys that are never used outside test code.
+  void RegisterKeysForTesting(flat_set<std::string> keys) {
+    test_keys_ = std::move(keys);
+  }
+
+ private:
+  virtual std::string GetValue(absl::string_view key) const = 0;
+
+  // Imaginary keys only used for testing.
+  flat_set<std::string> test_keys_;
+};
+
+}  // namespace webrtc
+
+#endif  // API_FIELD_TRIALS_REGISTRY_H_