Do not generalize field representations when making elements kind or observed transition.

src/objects.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_OBJECTS_H_
 #define V8_OBJECTS_H_
 
 #include <iosfwd>
 
 #include "src/allocation.h"
@@ skipping 6126 matching lines @@
                                               PropertyAttributes attributes,
                                               StoreFromKeyed store_mode);
   static Handle<Map> TransitionToAccessorProperty(
       Handle<Map> map, Handle<Name> name, AccessorComponent component,
       Handle<Object> accessor, PropertyAttributes attributes);
   static Handle<Map> ReconfigureDataProperty(Handle<Map> map, int descriptor,
                                              PropertyAttributes attributes);
 
   inline void AppendDescriptor(Descriptor* desc);
 
+  // Returns a copy of the map, prepared for inserting into the transition
+  // tree (if the |map| owns descriptors then the new one will share
+  // descriptors with |map|).
+  static Handle<Map> CopyForTransition(Handle<Map> map, const char* reason);
+
   // Returns a copy of the map, with all transitions dropped from the
   // instance descriptors.
   static Handle<Map> Copy(Handle<Map> map, const char* reason);
   static Handle<Map> Create(Isolate* isolate, int inobject_properties);
 
   // Returns the next free property index (only valid for FAST MODE).
   int NextFreePropertyIndex();
 
   // Returns the number of properties described in instance_descriptors
   // filtering out properties with the specified attributes.
@@ skipping 4777 matching lines @@
     } else {
       value &= ~(1 << bit_position);
     }
     return value;
   }
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_OBJECTS_H_