diff -r 000000000000 -r 6474c204b198 js/src/gc/Barrier.cpp
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/gc/Barrier.cpp	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,66 @@
+/* -*- 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/. */
+
+#include "gc/Barrier.h"
+
+#include "jscompartment.h"
+#include "jsobj.h"
+
+#include "gc/Zone.h"
+
+namespace js {
+
+#ifdef DEBUG
+
+bool
+HeapValue::preconditionForSet(Zone *zone)
+{
+    if (!value.isMarkable())
+        return true;
+
+    return ZoneOfValue(value) == zone ||
+           zone->runtimeFromAnyThread()->isAtomsZone(ZoneOfValue(value));
+}
+
+bool
+HeapSlot::preconditionForSet(JSObject *owner, Kind kind, uint32_t slot)
+{
+    return kind == Slot
+         ? &owner->getSlotRef(slot) == this
+         : &owner->getDenseElement(slot) == (const Value *)this;
+}
+
+bool
+HeapSlot::preconditionForSet(Zone *zone, JSObject *owner, Kind kind, uint32_t slot)
+{
+    bool ok = kind == Slot
+            ? &owner->getSlotRef(slot) == this
+            : &owner->getDenseElement(slot) == (const Value *)this;
+    return ok && owner->zone() == zone;
+}
+
+void
+HeapSlot::preconditionForWriteBarrierPost(JSObject *obj, Kind kind, uint32_t slot, Value target)
+{
+    JS_ASSERT_IF(kind == Slot, obj->getSlotAddressUnchecked(slot)->get() == target);
+    JS_ASSERT_IF(kind == Element,
+                 static_cast<HeapSlot *>(obj->getDenseElements() + slot)->get() == target);
+}
+
+bool
+RuntimeFromMainThreadIsHeapMajorCollecting(JS::shadow::Zone *shadowZone)
+{
+    return shadowZone->runtimeFromMainThread()->isHeapMajorCollecting();
+}
+#endif // DEBUG
+
+bool
+StringIsPermanentAtom(JSString *str)
+{
+    return str->isPermanentAtom();
+}
+
+} // namespace js