ES6 symbols: turn symbols into a proper primitive type

src/runtime.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 496 matching lines @@
   RUNTIME_FUNCTION_LIST_DEBUG(F) \
   RUNTIME_FUNCTION_LIST_DEBUGGER_SUPPORT(F)
 
 // ----------------------------------------------------------------------------
 // INLINE_FUNCTION_LIST defines all inlined functions accessed
 // with a native call of the form %_name from within JS code.
 // Entries have the form F(name, number of arguments, number of return values).
 #define INLINE_FUNCTION_LIST(F) \
   F(IsSmi, 1, 1)                                                             \
   F(IsNonNegativeSmi, 1, 1)                                                  \
-  F(IsSymbol, 1, 1)                                                          \
   F(IsArray, 1, 1)                                                           \
   F(IsRegExp, 1, 1)                                                          \
   F(IsConstructCall, 0, 1)                                                   \
   F(CallFunction, -1 /* receiver + n args + function */, 1)                  \
   F(ArgumentsLength, 0, 1)                                                   \
   F(Arguments, 1, 1)                                                         \
   F(ValueOf, 1, 1)                                                           \
   F(SetValueOf, 2, 1)                                                        \
   F(DateField, 2 /* date object, field index */, 1)                          \
   F(StringCharFromCode, 1, 1)                                                \
@@ skipping 190 matching lines @@
 //---------------------------------------------------------------------------
 // Constants used by interface to runtime functions.
 
 class DeclareGlobalsEvalFlag:     public BitField<bool,         0, 1> {};
 class DeclareGlobalsNativeFlag:   public BitField<bool,         1, 1> {};
 class DeclareGlobalsLanguageMode: public BitField<LanguageMode, 2, 2> {};
 
 } }  // namespace v8::internal
 
 #endif  // V8_RUNTIME_H_