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

src/objects-debug.cc

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Redistribution and use in source and binary forms, with or without
 // modification, are permitted provided that the following conditions are
 // met:
 //
 //     * Redistributions of source code must retain the above copyright
 //       notice, this list of conditions and the following disclaimer.
 //     * Redistributions in binary form must reproduce the above
 //       copyright notice, this list of conditions and the following
 //       disclaimer in the documentation and/or other materials provided
@@ skipping 935 matching lines @@
             return false;
           }
         }
         break;
       }
       case NORMAL:
       case FIELD:
       case CONSTANT_FUNCTION:
       case HANDLER:
       case INTERCEPTOR:
-      case NULL_DESCRIPTOR:
+        break;
+      case NONEXISTENT:
+        UNREACHABLE();
         break;
     }
   }
   return true;
 }
 
 
 void JSFunctionResultCache::JSFunctionResultCacheVerify() {
   JSFunction::cast(get(kFactoryIndex))->Verify();
 
@@ skipping 48 matching lines @@
   FixedArray* proto_transitions = prototype_transitions();
   MemsetPointer(proto_transitions->data_start(),
                 GetHeap()->the_hole_value(),
                 proto_transitions->length());
 }
 
 
 #endif  // DEBUG
 
 } }  // namespace v8::internal