[es6] call ToString() on template substitutions

src/ast-value-factory.h

 // Copyright 2014 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 243 matching lines @@
   F(make_reference_error, "MakeReferenceErrorEmbedded")                    \
   F(make_syntax_error, "MakeSyntaxErrorEmbedded")                          \
   F(make_type_error, "MakeTypeErrorEmbedded")                              \
   F(native, "native")                                                      \
   F(new_target, "new.target")                                              \
   F(next, "next")                                                          \
   F(proto, "__proto__")                                                    \
   F(prototype, "prototype")                                                \
   F(this, "this")                                                          \
   F(throw_iterator_result_not_an_object, "ThrowIteratorResultNotAnObject") \
+  F(to_string, "ToString")                                                 \
   F(use_asm, "use asm")                                                    \
   F(use_strong, "use strong")                                              \
   F(use_strict, "use strict")                                              \
   F(value, "value")
 
 #define OTHER_CONSTANTS(F) \
   F(true_value)            \
   F(false_value)           \
   F(null_value)            \
   F(undefined_value)       \
@@ skipping 83 matching lines @@
 #define F(name) AstValue* name##_;
   OTHER_CONSTANTS(F)
 #undef F
 };
 } }  // namespace v8::internal
 
 #undef STRING_CONSTANTS
 #undef OTHER_CONSTANTS
 
 #endif  // V8_AST_VALUE_FACTORY_H_