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diff --git a/js/src/ds/TraceableFifo.h b/js/src/ds/TraceableFifo.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 4 -*-
+ * vim: set ts=8 sts=4 et sw=4 tw=99:
+ * This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef js_TraceableFifo_h
+#define js_TraceableFifo_h
+
+#include "ds/Fifo.h"
+#include "js/RootingAPI.h"
+#include "js/TracingAPI.h"
+
+namespace js {
+
+// A TraceableFifo is a Fifo with an additional trace method that knows how to
+// visit all of the items stored in the Fifo. For Fifos that contain GC things,
+// this is usually more convenient than manually iterating and marking the
+// contents.
+//
+// Most types of GC pointers as keys and values can be traced with no extra
+// infrastructure. For structs and non-gc-pointer members, ensure that there is
+// a specialization of GCPolicy<T> with an appropriate trace method available
+// to handle the custom type. Generic helpers can be found in
+// js/public/TracingAPI.h. Generic helpers can be found in
+// js/public/TracingAPI.h.
+//
+// Note that although this Fifo's trace will deal correctly with moved items, it
+// does not itself know when to barrier or trace items. To function properly it
+// must either be used with Rooted, or barriered and traced manually.
+template <typename T,
+          size_t MinInlineCapacity = 0,
+          typename AllocPolicy = TempAllocPolicy>
+class TraceableFifo : public js::Fifo<T, MinInlineCapacity, AllocPolicy>
+{
+    using Base = js::Fifo<T, MinInlineCapacity, AllocPolicy>;
+
+  public:
+    explicit TraceableFifo(AllocPolicy alloc = AllocPolicy()) : Base(alloc) {}
+
+    TraceableFifo(TraceableFifo&& rhs) : Base(mozilla::Move(rhs)) { }
+    TraceableFifo& operator=(TraceableFifo&& rhs) { return Base::operator=(mozilla::Move(rhs)); }
+
+    TraceableFifo(const TraceableFifo&) = delete;
+    TraceableFifo& operator=(const TraceableFifo&) = delete;
+
+    void trace(JSTracer* trc) {
+        for (size_t i = 0; i < this->front_.length(); ++i)
+            JS::GCPolicy<T>::trace(trc, &this->front_[i], "fifo element");
+        for (size_t i = 0; i < this->rear_.length(); ++i)
+            JS::GCPolicy<T>::trace(trc, &this->rear_[i], "fifo element");
+    }
+};
+
+template <typename Outer, typename T, size_t Capacity, typename AllocPolicy>
+class TraceableFifoOperations
+{
+    using TF = TraceableFifo<T, Capacity, AllocPolicy>;
+    const TF& fifo() const { return static_cast<const Outer*>(this)->extract(); }
+
+  public:
+    size_t length() const { return fifo().length(); }
+    bool empty() const { return fifo().empty(); }
+    const T& front() const { return fifo().front(); }
+};
+
+template <typename Outer, typename T, size_t Capacity, typename AllocPolicy>
+class MutableTraceableFifoOperations
+  : public TraceableFifoOperations<Outer, T, Capacity, AllocPolicy>
+{
+    using TF = TraceableFifo<T, Capacity, AllocPolicy>;
+    TF& fifo() { return static_cast<Outer*>(this)->extract(); }
+
+  public:
+    T& front() { return fifo().front(); }
+
+    template<typename U> bool pushBack(U&& u) { return fifo().pushBack(mozilla::Forward<U>(u)); }
+    template<typename... Args> bool emplaceBack(Args&&... args) {
+        return fifo().emplaceBack(mozilla::Forward<Args...>(args...));
+    }
+
+    bool popFront() { return fifo().popFront(); }
+    void clear() { fifo().clear(); }
+};
+
+template <typename A, size_t B, typename C>
+class RootedBase<TraceableFifo<A,B,C>>
+  : public MutableTraceableFifoOperations<JS::Rooted<TraceableFifo<A,B,C>>, A,B,C>
+{
+    using TF = TraceableFifo<A,B,C>;
+
+    friend class TraceableFifoOperations<JS::Rooted<TF>, A,B,C>;
+    const TF& extract() const { return *static_cast<const JS::Rooted<TF>*>(this)->address(); }
+
+    friend class MutableTraceableFifoOperations<JS::Rooted<TF>, A,B,C>;
+    TF& extract() { return *static_cast<JS::Rooted<TF>*>(this)->address(); }
+};
+
+template <typename A, size_t B, typename C>
+class MutableHandleBase<TraceableFifo<A,B,C>>
+  : public MutableTraceableFifoOperations<JS::MutableHandle<TraceableFifo<A,B,C>>, A,B,C>
+{
+    using TF = TraceableFifo<A,B,C>;
+
+    friend class TraceableFifoOperations<JS::MutableHandle<TF>, A,B,C>;
+    const TF& extract() const {
+        return *static_cast<const JS::MutableHandle<TF>*>(this)->address();
+    }
+
+    friend class MutableTraceableFifoOperations<JS::MutableHandle<TF>, A,B,C>;
+    TF& extract() { return *static_cast<JS::MutableHandle<TF>*>(this)->address(); }
+};
+
+template <typename A, size_t B, typename C>
+class HandleBase<TraceableFifo<A,B,C>>
+  : public TraceableFifoOperations<JS::Handle<TraceableFifo<A,B,C>>, A,B,C>
+{
+    using TF = TraceableFifo<A,B,C>;
+
+    friend class TraceableFifoOperations<JS::Handle<TF>, A,B,C>;
+    const TF& extract() const {
+        return *static_cast<const JS::Handle<TF>*>(this)->address();
+    }
+};
+
+} // namespace js
+
+#endif // js_TraceableFifo_h