In-place shrinking of descriptor arrays with non-live transitions.

src/property-details.h

Index: src/property-details.h
diff --git a/src/property-details.h b/src/property-details.h
index a623fe9b1a4d5f8c68ea76e3939eb54aa649f16a..f3455841d69d2a8f902491eb11ec6395df0bb530 100644
--- a/src/property-details.h
+++ b/src/property-details.h
@@ -64,11 +64,8 @@ enum PropertyType {
   // All properties before MAP_TRANSITION are real.
   MAP_TRANSITION            = 6,  // only in fast mode
   CONSTANT_TRANSITION       = 7,  // only in fast mode
-  NULL_DESCRIPTOR           = 8,  // only in fast mode
-  // There are no IC stubs for NULL_DESCRIPTORS. Therefore,
-  // NULL_DESCRIPTOR can be used as the type flag for IC stubs for
-  // nonexistent properties.
-  NONEXISTENT = NULL_DESCRIPTOR
+  // Used as the type flag for IC stubs for nonexistent properties.
+  NONEXISTENT               = 8
 };