Fastpath some spread-call desugaring.

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 64f883bb4dd88500e28cb0451dc98aa7a603ddc8..10d3589ba573a8328eb0ff5afabdcbf46d59b1de 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -224,6 +224,8 @@ enum ContextLookupFlags {
   V(GENERATOR_FUNCTION_FUNCTION_INDEX, JSFunction,                             \
     generator_function_function)                                               \
   V(GENERATOR_OBJECT_PROTOTYPE_MAP_INDEX, Map, generator_object_prototype_map) \
+  V(INITIAL_ARRAY_ITERATOR_PROTOTYPE_INDEX, JSObject,                          \
+    initial_array_iterator_prototype)                                          \
   V(INITIAL_ARRAY_PROTOTYPE_INDEX, JSObject, initial_array_prototype)          \
   V(INITIAL_GENERATOR_PROTOTYPE_INDEX, JSObject, initial_generator_prototype)  \
   V(INITIAL_ITERATOR_PROTOTYPE_INDEX, JSObject, initial_iterator_prototype)    \