[serializer] ensure that immortal immovable roots are correctly deserialized.

src/objects.cc

 // Copyright 2015 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/objects.h"
 
 #include <cmath>
 #include <iomanip>
 #include <sstream>
 
@@ skipping 13473 matching lines @@
   // duplicates.
   Handle<Object> list;
   if (script_object->IsScript()) {
     Handle<Script> script = Handle<Script>::cast(script_object);
     list = handle(script->shared_function_infos(), isolate);
   } else {
     list = isolate->factory()->noscript_shared_function_infos();
   }
 
 #ifdef DEBUG
-  {
+  if (FLAG_enable_slow_asserts) {
     WeakFixedArray::Iterator iterator(*list);
     SharedFunctionInfo* next;
     while ((next = iterator.Next<SharedFunctionInfo>())) {
       DCHECK_NE(next, *shared);
     }
   }
 #endif  // DEBUG
   list = WeakFixedArray::Add(list, shared);
 
   if (script_object->IsScript()) {
@@ skipping 6229 matching lines @@
   if (cell->value() != *new_value) {
     cell->set_value(*new_value);
     Isolate* isolate = cell->GetIsolate();
     cell->dependent_code()->DeoptimizeDependentCodeGroup(
         isolate, DependentCode::kPropertyCellChangedGroup);
   }
 }
 
 }  // namespace internal
 }  // namespace v8