Native context: do not put public symbols and flags on the js builtins object.

src/prologue.js

 // Copyright 2015 the V8 project authors. All rights reserved.
 // Use of this source code is governed by a BSD-style license that can be
 // found in the LICENSE file.
 
 (function(global, utils) {
 
 "use strict";
 
 %CheckIsBootstrapping();
 
 // -----------------------------------------------------------------------
 // Utils
 
 var imports = UNDEFINED;
 var imports_from_experimental = UNDEFINED;
-var exports_container = {};
+var exports_container = %ExportFromRuntime({});
 
 // Export to other scripts.
 // In normal natives, this exports functions to other normal natives.
 // In experimental natives, this exports to other experimental natives and
 // to normal natives that import using utils.ImportFromExperimental.
 function Export(f) {
   f(exports_container);
 }
 
 
 // Import from other scripts. The actual importing happens in PostNatives and
 // PostExperimental so that we can import from scripts executed later. However,
 // that means that the import is not available until the very end. If the
 // import needs to be available immediate, use ImportNow.
 // In normal natives, this imports from other normal natives.
 // In experimental natives, this imports from other experimental natives and
 // whitelisted exports from normal natives.
 function Import(f) {
   f.next = imports;
   imports = f;
 }
 
+
 // Import immediately from exports of previous scripts. We need this for
 // functions called during bootstrapping. Hooking up imports in PostNatives
 // would be too late.
-function ImportNow(f) {
-  f(exports_container);
+function ImportNow(name) {
+  return exports_container[name];
 }
 
 
 // In normal natives, import from experimental natives.
 // Not callable from experimental natives.
 function ImportFromExperimental(f) {
   f.next = imports_from_experimental;
   imports_from_experimental = f;
 }
 
@@ skipping 88 matching lines @@
     var key = methods[i];
     var f = methods[i + 1];
     %AddNamedProperty(prototype, key, f, DONT_ENUM | DONT_DELETE | READ_ONLY);
     %SetNativeFlag(f);
   }
   %InternalSetPrototype(prototype, null);
   %ToFastProperties(prototype);
 }
 
 
-var private_symbols = %ExportPrivateSymbols({});
-
-function GetPrivateSymbol(name) {
-  return private_symbols[name];
-}
-
 // -----------------------------------------------------------------------
 // To be called by bootstrapper
 
 function PostNatives(utils) {
   %CheckIsBootstrapping();
 
   for ( ; !IS_UNDEFINED(imports); imports = imports.next) {
     imports(exports_container);
   }
 
@@ skipping 15 matching lines @@
     "InnerArrayReverse",
     "InnerArraySome",
     "InnerArraySort",
     "InnerArrayToLocaleString",
     "IsNaN",
     "MathMax",
     "MathMin",
     "ObjectIsFrozen",
     "ObjectDefineProperty",
     "OwnPropertyKeys",
+    "SymbolToString",
     "ToNameArray",
     "ToBoolean",
     "ToNumber",
     "ToString",
+    // From runtime:
+    "is_concat_spreadable_symbol",
+    "iterator_symbol",
+    "promise_status_symbol",
+    "promise_value_symbol",
+    "reflect_apply",
+    "reflect_construct",
+    "to_string_tag_symbol",
   ];
 
   var filtered_exports = {};
   %OptimizeObjectForAddingMultipleProperties(
       filtered_exports, expose_list.length);
   for (var key of expose_list) {
     filtered_exports[key] = exports_container[key];
   }
   %ToFastProperties(filtered_exports);
   exports_container = filtered_exports;
 
   utils.PostNatives = UNDEFINED;
   utils.ImportFromExperimental = UNDEFINED;
 }
 
 
 function PostExperimentals(utils) {
   %CheckIsBootstrapping();
-
+  %ExportExperimentalFromRuntime(exports_container);
   for ( ; !IS_UNDEFINED(imports); imports = imports.next) {
     imports(exports_container);
   }
   for ( ; !IS_UNDEFINED(imports_from_experimental);
           imports_from_experimental = imports_from_experimental.next) {
     imports_from_experimental(exports_container);
   }
 
   exports_container = UNDEFINED;
-  private_symbols = UNDEFINED;
 
   utils.PostExperimentals = UNDEFINED;
   utils.PostDebug = UNDEFINED;
   utils.Import = UNDEFINED;
   utils.Export = UNDEFINED;
 }
 
 
 function PostDebug(utils) {
   for ( ; !IS_UNDEFINED(imports); imports = imports.next) {
     imports(exports_container);
   }
 
   exports_container = UNDEFINED;
-  private_symbols = UNDEFINED;
 
   utils.PostDebug = UNDEFINED;
   utils.PostExperimentals = UNDEFINED;
   utils.Import = UNDEFINED;
   utils.Export = UNDEFINED;
 }
 
 // -----------------------------------------------------------------------
 
-%OptimizeObjectForAddingMultipleProperties(utils, 14);
+%OptimizeObjectForAddingMultipleProperties(utils, 13);
 
 utils.Import = Import;
 utils.ImportNow = ImportNow;
 utils.Export = Export;
 utils.ImportFromExperimental = ImportFromExperimental;
-utils.GetPrivateSymbol = GetPrivateSymbol;
 utils.SetFunctionName = SetFunctionName;
 utils.InstallConstants = InstallConstants;
 utils.InstallFunctions = InstallFunctions;
 utils.InstallGetter = InstallGetter;
 utils.InstallGetterSetter = InstallGetterSetter;
 utils.SetUpLockedPrototype = SetUpLockedPrototype;
 utils.PostNatives = PostNatives;
 utils.PostExperimentals = PostExperimentals;
 utils.PostDebug = PostDebug;
 
 %ToFastProperties(utils);
 
 })