Replace HeapNumber as doublebox with an explicit MutableHeapNumber.

src/objects-visiting.cc

 // Copyright 2011 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.
 
 #include "src/v8.h"
 
 #include "src/ic-inl.h"
 #include "src/objects-visiting.h"
 
 namespace v8 {
@@ skipping 130 matching lines @@
     case JS_SET_ITERATOR_TYPE:
     case JS_MAP_ITERATOR_TYPE:
       return GetVisitorIdForSize(kVisitJSObject,
                                  kVisitJSObjectGeneric,
                                  instance_size);
 
     case JS_FUNCTION_TYPE:
       return kVisitJSFunction;
 
     case HEAP_NUMBER_TYPE:
+    case MUTABLE_HEAP_NUMBER_TYPE:
 #define EXTERNAL_ARRAY_CASE(Type, type, TYPE, ctype, size)                     \
     case EXTERNAL_##TYPE##_ARRAY_TYPE:
 
     TYPED_ARRAYS(EXTERNAL_ARRAY_CASE)
       return GetVisitorIdForSize(kVisitDataObject,
                                  kVisitDataObjectGeneric,
                                  instance_size);
 #undef EXTERNAL_ARRAY_CASE
 
     case FIXED_UINT8_ARRAY_TYPE:
@@ skipping 289 matching lines @@
 
 
 template Object* VisitWeakList<JSArrayBuffer>(
     Heap* heap, Object* list, WeakObjectRetainer* retainer);
 
 
 template Object* VisitWeakList<AllocationSite>(
     Heap* heap, Object* list, WeakObjectRetainer* retainer);
 
 } }  // namespace v8::internal