[runtime] Add PropertyConstness bit to PropertyDetails.

src/map-updater.h

Index: src/map-updater.h
diff --git a/src/map-updater.h b/src/map-updater.h
index 68b720365b1e86aa741b3e17a5658f9ea3b598f4..39e432dd03f07316d8f5ba74faa2ff84532e3f23 100644
--- a/src/map-updater.h
+++ b/src/map-updater.h
@@ -157,6 +157,7 @@ class MapUpdater {
   int modified_descriptor_ = -1;
   PropertyKind new_kind_ = kData;
   PropertyAttributes new_attributes_ = NONE;
+  PropertyConstness new_constness_ = kMutable;
   PropertyLocation new_location_ = kField;
   Representation new_representation_ = Representation::None();