Add support for per-isolate private symbols

src/symbol.js

 // Copyright 2013 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 47 matching lines @@
   if (!(IS_SYMBOL(this) || IS_SYMBOL_WRAPPER(this))) {
     throw MakeTypeError(
       'incompatible_method_receiver', ["Symbol.prototype.valueOf", this]);
   }
   return %_ValueOf(this);
 }
 
 
 function GetSymbolRegistry() {
   var registry = %SymbolRegistry();
-  if (!('internal' in registry)) {
-    registry.internal = {__proto__: null};
+  if (!('for' in registry)) {
     registry.for = {__proto__: null};
+    registry.for_intern = {__proto__: null};
     registry.keyFor = {__proto__: null};
+    // Other members are added and used in runtime and API functions:
+    // registry.private_intern
+    // registry.private_api
   }
   return registry;
 }
 
 
 function InternalSymbol(key) {
   var registry = GetSymbolRegistry();
-  if (!(key in registry.internal)) {
-    registry.internal[key] = %CreateSymbol(key);
+  if (!(key in registry.for_intern)) {
+    registry.for_intern[key] = %CreateSymbol(key);
   }
-  return registry.internal[key];
+  return registry.for_intern[key];
 }
 
 
 function SymbolFor(key) {
   key = TO_STRING_INLINE(key);
   var registry = GetSymbolRegistry();
   if (!(key in registry.for)) {
     var symbol = %CreateSymbol(key);
     registry.for[key] = symbol;
     registry.keyFor[symbol] = key;
@@ skipping 67 matching lines @@
 
 function ExtendObject() {
   %CheckIsBootstrapping();
 
   InstallFunctions($Object, DONT_ENUM, $Array(
     "getOwnPropertySymbols", ObjectGetOwnPropertySymbols
   ));
 }
 
 ExtendObject();