Allow race-full access of map instance size when sweeping concurrently.

src/objects.h

 // 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 5968 matching lines @@
 //  - Size information about the object
 //  - How to iterate over an object (for garbage collection)
 class Map: public HeapObject {
  public:
   // Instance size.
   // Size in bytes or kVariableSizeSentinel if instances do not have
   // a fixed size.
   inline int instance_size();
   inline void set_instance_size(int value);
 
+  // Get the instance size of a map using no barrier semantics.
+  inline int nobarrier_instance_size();
+
   // Count of properties allocated in the object.
   inline int inobject_properties();
   inline void set_inobject_properties(int value);
 
   // Count of property fields pre-allocated in the object when first allocated.
   inline int pre_allocated_property_fields();
   inline void set_pre_allocated_property_fields(int value);
 
   // Instance type.
   inline InstanceType instance_type();
@@ skipping 562 matching lines @@
   void VerifyOmittedMapChecks();
 #endif
 
   inline int visitor_id();
   inline void set_visitor_id(int visitor_id);
 
   typedef void (*TraverseCallback)(Map* map, void* data);
 
   void TraverseTransitionTree(TraverseCallback callback, void* data);
 
+  inline void Shrink(int slack);
+
   // When you set the prototype of an object using the __proto__ accessor you
   // need a new map for the object (the prototype is stored in the map).  In
   // order not to multiply maps unnecessarily we store these as transitions in
   // the original map.  That way we can transition to the same map if the same
   // prototype is set, rather than creating a new map every time.  The
   // transitions are in the form of a map where the keys are prototype objects
   // and the values are the maps the are transitioned to.
   static const int kMaxCachedPrototypeTransitions = 256;
   static Handle<Map> GetPrototypeTransition(Handle<Map> map,
                                             Handle<Object> prototype);
@@ skipping 4405 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_