Fix and test use of property descriptor objects.

src/contexts.h

Index: src/contexts.h
diff --git a/src/contexts.h b/src/contexts.h
index 53b40f127d8efac2f45ebfdca2dd55d116cf945b..ff2b968a27aed84a690c701d974b7e5b7fe715c7 100644
--- a/src/contexts.h
+++ b/src/contexts.h
@@ -110,6 +110,8 @@ enum ContextLookupFlags {
   V(MAP_CACHE_INDEX, Object, map_cache) \
   V(CONTEXT_DATA_INDEX, Object, data) \
   V(ALLOW_CODE_GEN_FROM_STRINGS_INDEX, Object, allow_code_gen_from_strings) \
+  V(TO_COMPLETE_PROPERTY_DESCRIPTOR_INDEX, JSFunction, \
+    to_complete_property_descriptor) \
   V(DERIVED_HAS_TRAP_INDEX, JSFunction, derived_has_trap) \
   V(DERIVED_GET_TRAP_INDEX, JSFunction, derived_get_trap) \
   V(DERIVED_SET_TRAP_INDEX, JSFunction, derived_set_trap)
@@ -228,6 +230,7 @@ class Context: public FixedArray {
     OUT_OF_MEMORY_INDEX,
     CONTEXT_DATA_INDEX,
     ALLOW_CODE_GEN_FROM_STRINGS_INDEX,
+    TO_COMPLETE_PROPERTY_DESCRIPTOR_INDEX,
     DERIVED_HAS_TRAP_INDEX,
     DERIVED_GET_TRAP_INDEX,
     DERIVED_SET_TRAP_INDEX,