Improve JSON stringifier's escape check.

src/heap.h

 // 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 138 matching lines @@
   V(FixedArray, natives_source_cache, NativesSourceCache)                      \
   V(Object, last_script_id, LastScriptId)                                      \
   V(Script, empty_script, EmptyScript)                                         \
   V(Smi, real_stack_limit, RealStackLimit)                                     \
   V(StringDictionary, intrinsic_function_names, IntrinsicFunctionNames)        \
   V(Smi, arguments_adaptor_deopt_pc_offset, ArgumentsAdaptorDeoptPCOffset)     \
   V(Smi, construct_stub_deopt_pc_offset, ConstructStubDeoptPCOffset)           \
   V(Smi, getter_stub_deopt_pc_offset, GetterStubDeoptPCOffset)                 \
   V(Smi, setter_stub_deopt_pc_offset, SetterStubDeoptPCOffset)                 \
   V(JSObject, observation_state, ObservationState)                             \
-  V(Map, external_map, ExternalMap)
+  V(Map, external_map, ExternalMap)                                            \
+  V(Map, printable_ascii_symbol_map, PrintableAsciiSymbolMap)
 
 #define ROOT_LIST(V)                                  \
   STRONG_ROOT_LIST(V)                                 \
   V(SymbolTable, symbol_table, SymbolTable)
 
 #define SYMBOL_LIST(V)                                                   \
   V(Array_symbol, "Array")                                               \
   V(Object_symbol, "Object")                                             \
   V(Proto_symbol, "__proto__")                                           \
   V(StringImpl_symbol, "StringImpl")                                     \
@@ skipping 2775 matching lines @@
   AssertNoAllocation no_alloc;  // i.e. no gc allowed.
 
  private:
   DISALLOW_IMPLICIT_CONSTRUCTORS(PathTracer);
 };
 #endif  // DEBUG
 
 } }  // namespace v8::internal
 
 #endif  // V8_HEAP_H_