Replace ad-hoc weakness in prototype transitions with WeakCell.

src/transitions.h

 // Copyright 2012 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 #ifndef V8_TRANSITIONS_H_
 #define V8_TRANSITIONS_H_
 
 #include "src/checks.h"
 #include "src/elements-kind.h"
 #include "src/heap/heap.h"
@@ skipping 74 matching lines @@
   // 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 they transition to.
   // Cache format:
   //    0: finger - index of the first free cell in the cache
   //    1 + i: target map
   static const int kMaxCachedPrototypeTransitions = 256;
-  static Handle<Map> PutPrototypeTransition(Handle<Map> map,
-                                            Handle<Object> prototype,
-                                            Handle<Map> target_map);
+  static void PutPrototypeTransition(Handle<Map> map, Handle<Object> prototype,
+                                     Handle<Map> target_map);
 
   static Handle<Map> GetPrototypeTransition(Handle<Map> map,
                                             Handle<Object> prototype);
 
   static FixedArray* GetPrototypeTransitions(Map* map);
 
   static int NumberOfPrototypeTransitions(FixedArray* proto_transitions) {
     if (proto_transitions->length() == 0) return 0;
     Object* raw = proto_transitions->get(kProtoTransitionNumberOfEntriesOffset);
     return Smi::cast(raw)->value();
@@ skipping 191 matching lines @@
                                                Object* transitions);
 #endif
 
   DISALLOW_IMPLICIT_CONSTRUCTORS(TransitionArray);
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_TRANSITIONS_H_