Improve JSON stringifier's escape check.

src/heap.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 2380 matching lines @@
   set_foreign_map(Map::cast(obj));
 
   for (unsigned i = 0; i < ARRAY_SIZE(string_type_table); i++) {
     const StringTypeTable& entry = string_type_table[i];
     { MaybeObject* maybe_obj = AllocateMap(entry.type, entry.size);
       if (!maybe_obj->ToObject(&obj)) return false;
     }
     roots_[entry.index] = Map::cast(obj);
   }
 
+  { MaybeObject* maybe_obj = AllocateMap(ASCII_SYMBOL_TYPE,
+                                         kVariableSizeSentinel);
+    if (!maybe_obj->ToObject(&obj)) return false;
+  }
+  set_printable_ascii_symbol_map(Map::cast(obj));
+
   { MaybeObject* maybe_obj = AllocateMap(STRING_TYPE, kVariableSizeSentinel);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
   set_undetectable_string_map(Map::cast(obj));
   Map::cast(obj)->set_is_undetectable();
 
   { MaybeObject* maybe_obj =
         AllocateMap(ASCII_STRING_TYPE, kVariableSizeSentinel);
     if (!maybe_obj->ToObject(&obj)) return false;
   }
@@ skipping 5126 matching lines @@
       static_cast<int>(object_sizes_last_time_[index]));
   FIXED_ARRAY_SUB_INSTANCE_TYPE_LIST(ADJUST_LAST_TIME_OBJECT_COUNT)
 #undef ADJUST_LAST_TIME_OBJECT_COUNT
 
   memcpy(object_counts_last_time_, object_counts_, sizeof(object_counts_));
   memcpy(object_sizes_last_time_, object_sizes_, sizeof(object_sizes_));
   ClearObjectStats();
 }
 
 } }  // namespace v8::internal