Bug 1244252 - Don't check object group generation when generating code to create unboxed objects off thread, r=terrence.

js/src/jit/MacroAssembler.cpp

@@ -1173,7 +1173,7 @@ MacroAssembler::initGCThing(Register obj, Register temp, JSObject* templateObj,
 void
 MacroAssembler::initUnboxedObjectContents(Register object, UnboxedPlainObject* templateObject)
 {
-    const UnboxedLayout& layout = templateObject->layout();
+    const UnboxedLayout& layout = templateObject->layoutDontCheckGeneration();
 
     // Initialize reference fields of the object, per UnboxedPlainObject::create.
     if (const int32_t* list = layout.traceList()) {