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diff --git a/third_party/abseil_cpp/absl/random/internal/mocking_bit_gen_base.h b/third_party/abseil_cpp/absl/random/internal/mocking_bit_gen_base.h
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+++ b/third_party/abseil_cpp/absl/random/internal/mocking_bit_gen_base.h
@@ -0,0 +1,85 @@
+//
+// Copyright 2018 The Abseil Authors.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//      https://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+//
+#ifndef ABSL_RANDOM_INTERNAL_MOCKING_BIT_GEN_BASE_H_
+#define ABSL_RANDOM_INTERNAL_MOCKING_BIT_GEN_BASE_H_
+
+#include <string>
+#include <typeinfo>
+
+#include "absl/random/random.h"
+#include "absl/strings/str_cat.h"
+
+namespace absl {
+ABSL_NAMESPACE_BEGIN
+namespace random_internal {
+
+class MockingBitGenBase {
+  template <typename>
+  friend struct DistributionCaller;
+  using generator_type = absl::BitGen;
+
+ public:
+  // URBG interface
+  using result_type = generator_type::result_type;
+  static constexpr result_type(min)() { return (generator_type::min)(); }
+  static constexpr result_type(max)() { return (generator_type::max)(); }
+  result_type operator()() { return gen_(); }
+
+  virtual ~MockingBitGenBase() = default;
+
+ protected:
+  // CallImpl is the type-erased virtual dispatch.
+  // The type of dist is always distribution<T>,
+  // The type of result is always distribution<T>::result_type.
+  virtual bool CallImpl(const std::type_info& distr_type, void* dist_args,
+                        void* result) = 0;
+
+  template <typename DistrT, typename ArgTupleT>
+  static const std::type_info& GetTypeId() {
+    return typeid(std::pair<absl::decay_t<DistrT>, absl::decay_t<ArgTupleT>>);
+  }
+
+  // Call the generating distribution function.
+  // Invoked by DistributionCaller<>::Call<DistT>.
+  // DistT is the distribution type.
+  template <typename DistrT, typename... Args>
+  typename DistrT::result_type Call(Args&&... args) {
+    using distr_result_type = typename DistrT::result_type;
+    using ArgTupleT = std::tuple<absl::decay_t<Args>...>;
+
+    ArgTupleT arg_tuple(std::forward<Args>(args)...);
+    auto dist = absl::make_from_tuple<DistrT>(arg_tuple);
+
+    distr_result_type result{};
+    bool found_match =
+        CallImpl(GetTypeId<DistrT, ArgTupleT>(), &arg_tuple, &result);
+
+    if (!found_match) {
+      result = dist(gen_);
+    }
+
+    return result;
+  }
+
+ private:
+  generator_type gen_;
+};  // namespace random_internal
+
+}  // namespace random_internal
+ABSL_NAMESPACE_END
+}  // namespace absl
+
+#endif  // ABSL_RANDOM_INTERNAL_MOCKING_BIT_GEN_BASE_H_