ES6 symbols: turn symbols into a proper primitive type

src/code-stubs.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 1470 matching lines @@
 
 class ToBooleanStub: public PlatformCodeStub {
  public:
   enum Type {
     UNDEFINED,
     BOOLEAN,
     NULL_TYPE,
     SMI,
     SPEC_OBJECT,
     STRING,
+    SYMBOL,
     HEAP_NUMBER,
     NUMBER_OF_TYPES
   };
 
   // At most 8 different types can be distinguished, because the Code object
   // only has room for a single byte to hold a set of these types. :-P
   STATIC_ASSERT(NUMBER_OF_TYPES <= 8);
 
   class Types {
    public:
@@ skipping 159 matching lines @@
 
   // The current function entry hook.
   static FunctionEntryHook entry_hook_;
 
   DISALLOW_COPY_AND_ASSIGN(ProfileEntryHookStub);
 };
 
 } }  // namespace v8::internal
 
 #endif  // V8_CODE_STUBS_H_