Replace HeapNumber as doublebox with an explicit MutableHeapNumber.

src/ic.cc

 // 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 1846 matching lines @@
   // Expand the properties array.
   FixedArray* old_storage = object->properties();
   int new_unused = transition->unused_property_fields();
   int new_size = old_storage->length() + new_unused + 1;
   Object* result;
   MaybeObject* maybe_result = old_storage->CopySize(new_size);
   if (!maybe_result->ToObject(&result)) return maybe_result;
 
   FixedArray* new_storage = FixedArray::cast(result);
 
-  Object* to_store = value;
-
   DescriptorArray* descriptors = transition->instance_descriptors();
   PropertyDetails details = descriptors->GetDetails(transition->LastAdded());
-  if (details.representation().IsDouble()) {
-    MaybeObject* maybe_storage =
-        isolate->heap()->AllocateHeapNumber(value->Number());
-    if (!maybe_storage->To(&to_store)) return maybe_storage;
-  }
+  Object* to_store;
+  MaybeObject* maybe_storage = value->AllocateNewStorageFor(
+      isolate->heap(), details.representation());
+  if (!maybe_storage->To(&to_store)) return maybe_storage;
 
   new_storage->set(old_storage->length(), to_store);
 
   // Set the new property value and do the map transition.
   object->set_properties(new_storage);
   object->set_map(transition);
 
   // Return the stored value.
   return value;
 }
@@ skipping 952 matching lines @@
 #undef ADDR
 };
 
 
 Address IC::AddressFromUtilityId(IC::UtilityId id) {
   return IC_utilities[id];
 }
 
 
 } }  // namespace v8::internal