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diff --git a/js/src/irregexp/util/FlagsShim.h b/js/src/irregexp/util/FlagsShim.h
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+++ b/js/src/irregexp/util/FlagsShim.h
@@ -0,0 +1,93 @@
+// Copyright 2014 the V8 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.
+
+#ifndef V8_UTIL_FLAGS_H_
+#define V8_UTIL_FLAGS_H_
+
+// Origin:
+// https://github.com/v8/v8/blob/1bafcc6b999b23ea1d394f5d267a08183e3c4e19/src/base/flags.h#L15-L90
+
+namespace v8 {
+namespace base {
+
+// The Flags class provides a type-safe way of storing OR-combinations of enum
+// values. The Flags<T, S> class is a template class, where T is an enum type,
+// and S is the underlying storage type (usually int).
+//
+// The traditional C++ approach for storing OR-combinations of enum values is to
+// use an int or unsigned int variable. The inconvenience with this approach is
+// that there's no type checking at all; any enum value can be OR'd with any
+// other enum value and passed on to a function that takes an int or unsigned
+// int.
+template <typename T, typename S = int>
+class Flags final {
+ public:
+  using flag_type = T;
+  using mask_type = S;
+
+  constexpr Flags() : mask_(0) {}
+  constexpr Flags(flag_type flag) : mask_(static_cast<S>(flag)) {}
+  constexpr explicit Flags(mask_type mask) : mask_(static_cast<S>(mask)) {}
+
+  constexpr bool operator==(flag_type flag) const {
+    return mask_ == static_cast<S>(flag);
+  }
+  constexpr bool operator!=(flag_type flag) const {
+    return mask_ != static_cast<S>(flag);
+  }
+
+  Flags& operator&=(const Flags& flags) {
+    mask_ &= flags.mask_;
+    return *this;
+  }
+  Flags& operator|=(const Flags& flags) {
+    mask_ |= flags.mask_;
+    return *this;
+  }
+  Flags& operator^=(const Flags& flags) {
+    mask_ ^= flags.mask_;
+    return *this;
+  }
+
+  constexpr Flags operator&(const Flags& flags) const {
+    return Flags(mask_ & flags.mask_);
+  }
+  constexpr Flags operator|(const Flags& flags) const {
+    return Flags(mask_ | flags.mask_);
+  }
+  constexpr Flags operator^(const Flags& flags) const {
+    return Flags(mask_ ^ flags.mask_);
+  }
+
+  Flags& operator&=(flag_type flag) { return operator&=(Flags(flag)); }
+  Flags& operator|=(flag_type flag) { return operator|=(Flags(flag)); }
+  Flags& operator^=(flag_type flag) { return operator^=(Flags(flag)); }
+
+  constexpr Flags operator&(flag_type flag) const {
+    return operator&(Flags(flag));
+  }
+  constexpr Flags operator|(flag_type flag) const {
+    return operator|(Flags(flag));
+  }
+  constexpr Flags operator^(flag_type flag) const {
+    return operator^(Flags(flag));
+  }
+
+  constexpr Flags operator~() const { return Flags(~mask_); }
+
+  constexpr operator mask_type() const { return mask_; }
+  constexpr bool operator!() const { return !mask_; }
+
+  Flags without(flag_type flag) { return *this & (~Flags(flag)); }
+
+  friend size_t hash_value(const Flags& flags) { return flags.mask_; }
+
+ private:
+  mask_type mask_;
+};
+
+}  // namespace base
+}  // namespace v8
+
+#endif  // V8_UTIL_FLAG_H_