Use mutable heapnumbers to store doubles in fields.

src/property.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 250 matching lines @@
     return JSProxy::cast(holder_);
   }
 
   PropertyType type() {
     ASSERT(IsFound());
     return details_.type();
   }
 
   Representation representation() {
     ASSERT(IsFound());
+    ASSERT(!IsTransition());
+    ASSERT(details_.type() != NONEXISTENT);
     return details_.representation();
   }
 
   PropertyAttributes GetAttributes() {
     ASSERT(!IsTransition());
     ASSERT(IsFound());
     ASSERT(details_.type() != NONEXISTENT);
     return details_.attributes();
   }
 
@@ skipping 211 matching lines @@
   JSReceiver* holder_;
   int number_;
   bool cacheable_;
   PropertyDetails details_;
 };
 
 
 } }  // namespace v8::internal
 
 #endif  // V8_PROPERTY_H_