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diff --git a/js/src/gc/Allocator.h b/js/src/gc/Allocator.h
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+/* -*- Mode: C++; tab-width: 8; indent-tabs-mode: nil; c-basic-offset: 2 -*-
+ * vim: set ts=8 sts=2 et sw=2 tw=80:
+ * 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 gc_Allocator_h
+#define gc_Allocator_h
+
+#include <stdint.h>
+
+#include "gc/AllocKind.h"
+#include "js/RootingAPI.h"
+
+class JSFatInlineString;
+
+namespace js {
+
+enum AllowGC { NoGC = 0, CanGC = 1 };
+
+namespace gc {
+
+/*
+ * This flag allows an allocation site to request a specific heap based upon the
+ * estimated lifetime or lifetime requirements of objects allocated from that
+ * site.
+ */
+enum InitialHeap : uint8_t { DefaultHeap, TenuredHeap };
+
+}  // namespace gc
+
+// Allocate a new GC thing that's not a JSObject or a string.
+//
+// After a successful allocation the caller must fully initialize the thing
+// before calling any function that can potentially trigger GC. This will ensure
+// that GC tracing never sees junk values stored in the partially initialized
+// thing.
+template <typename T, AllowGC allowGC = CanGC>
+T* Allocate(JSContext* cx);
+
+// Allocate a JSObject.
+//
+// A longer signature that includes additional information in support of various
+// optimizations. If dynamic slots are requested they will be allocated and the
+// pointer stored directly in |NativeObject::slots_|.
+template <AllowGC allowGC = CanGC>
+JSObject* AllocateObject(JSContext* cx, gc::AllocKind kind,
+                         size_t nDynamicSlots, gc::InitialHeap heap,
+                         const JSClass* clasp);
+
+// Internal function used for nursery-allocatable strings.
+template <typename StringAllocT, AllowGC allowGC = CanGC>
+StringAllocT* AllocateStringImpl(JSContext* cx, gc::InitialHeap heap);
+
+// Allocate a string.
+//
+// Use for nursery-allocatable strings. Returns a value cast to the correct
+// type.
+template <typename StringT, AllowGC allowGC = CanGC>
+StringT* AllocateString(JSContext* cx, gc::InitialHeap heap) {
+  return static_cast<StringT*>(AllocateStringImpl<JSString, allowGC>(cx, heap));
+}
+
+// Specialization for JSFatInlineString that must use a different allocation
+// type. Note that we have to explicitly specialize for both values of AllowGC
+// because partial function specialization is not allowed.
+template <>
+inline JSFatInlineString* AllocateString<JSFatInlineString, CanGC>(
+    JSContext* cx, gc::InitialHeap heap) {
+  return static_cast<JSFatInlineString*>(
+      js::AllocateStringImpl<JSFatInlineString, CanGC>(cx, heap));
+}
+
+template <>
+inline JSFatInlineString* AllocateString<JSFatInlineString, NoGC>(
+    JSContext* cx, gc::InitialHeap heap) {
+  return static_cast<JSFatInlineString*>(
+      js::AllocateStringImpl<JSFatInlineString, NoGC>(cx, heap));
+}
+
+// Allocate a BigInt.
+//
+// Use for nursery-allocatable BigInt.
+template <AllowGC allowGC = CanGC>
+JS::BigInt* AllocateBigInt(JSContext* cx, gc::InitialHeap heap);
+
+}  // namespace js
+
+#endif  // gc_Allocator_h