diff -r 000000000000 -r 6474c204b198 js/src/vm/ObjectImpl-inl.h
--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/js/src/vm/ObjectImpl-inl.h	Wed Dec 31 06:09:35 2014 +0100
@@ -0,0 +1,55 @@
+/* -*- 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 vm_ObjectImpl_inl_h
+#define vm_ObjectImpl_inl_h
+
+#include "vm/ObjectImpl.h"
+
+#include "jscntxt.h"
+#include "jsproxy.h"
+
+#include "vm/ProxyObject.h"
+#include "vm/TypedArrayObject.h"
+
+namespace js {
+
+/* static */ inline bool
+ObjectImpl::isExtensible(ExclusiveContext *cx, Handle<ObjectImpl*> obj, bool *extensible)
+{
+    if (obj->asObjectPtr()->is<ProxyObject>()) {
+        if (!cx->shouldBeJSContext())
+            return false;
+        HandleObject h =
+            HandleObject::fromMarkedLocation(reinterpret_cast<JSObject* const*>(obj.address()));
+        return Proxy::isExtensible(cx->asJSContext(), h, extensible);
+    }
+
+    *extensible = obj->nonProxyIsExtensible();
+    return true;
+}
+
+inline bool
+ClassCanHaveFixedData(const Class *clasp)
+{
+    // Normally, the number of fixed slots given an object is the maximum
+    // permitted for its size class. For array buffers and typed arrays we only
+    // use enough to cover the class reserved slots, so that the remaining
+    // space in the object's allocation is available for the buffer's data.
+    return clasp == &ArrayBufferObject::class_ || IsTypedArrayClass(clasp);
+}
+
+inline void *
+ObjectImpl::fixedData(size_t nslots) const
+{
+    JS_ASSERT(ClassCanHaveFixedData(getClass()));
+    JS_ASSERT(nslots == numFixedSlots() + (hasPrivate() ? 1 : 0));
+    return &fixedSlots()[nslots];
+}
+
+} // namespace js
+
+#endif /* vm_ObjectImpl_inl_h */