Use mutable heapnumbers to store doubles in fields.

src/builtins.h

 // Copyright 2011 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 106 matching lines @@
   V(LoadIC_Miss,                    BUILTIN, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
   V(KeyedLoadIC_Miss,               BUILTIN, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
   V(KeyedLoadIC_MissForceGeneric,   BUILTIN, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
   V(KeyedLoadIC_Slow,               BUILTIN, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
   V(StoreIC_Miss,                   BUILTIN, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
+  V(StoreIC_Slow,                   BUILTIN, UNINITIALIZED,             \
+                                    Code::kNoExtraICState)              \
   V(KeyedStoreIC_Miss,              BUILTIN, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
   V(KeyedStoreIC_MissForceGeneric,  BUILTIN, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
   V(KeyedStoreIC_Slow,              BUILTIN, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
   V(LoadIC_Initialize,              LOAD_IC, UNINITIALIZED,             \
                                     Code::kNoExtraICState)              \
   V(LoadIC_PreMonomorphic,          LOAD_IC, PREMONOMORPHIC,            \
                                     Code::kNoExtraICState)              \
@@ skipping 270 matching lines @@
 
   friend class BuiltinFunctionTable;
   friend class Isolate;
 
   DISALLOW_COPY_AND_ASSIGN(Builtins);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_BUILTINS_H_