[runtime] Add PropertyConstness bit to PropertyDetails.

src/lookup.cc

Index: src/lookup.cc
diff --git a/src/lookup.cc b/src/lookup.cc
index 1075f90e1685d93e4bfee98ecb12f6015cb16228..c3cf013c68f60cf102c7063035353a0f98d92db2 100644
--- a/src/lookup.cc
+++ b/src/lookup.cc
@@ -687,6 +687,7 @@ void LookupIterator::WriteDataValue(Handle<Object> value) {
                                             property_details_, *value);
     } else {
       DCHECK_EQ(kDescriptor, property_details_.location());
+      DCHECK_EQ(kConst, property_details_.constness());
     }
   } else if (holder->IsJSGlobalObject()) {
     GlobalDictionary* dictionary = JSObject::cast(*holder)->global_dictionary();