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

src/runtime.js

Index: src/runtime.js
diff --git a/src/runtime.js b/src/runtime.js
index 1ef4e973fdc8dd1baff155916e15b1e75155cc88..130b019de6cc640c4402ae2c06bf4f42fc85dcc4 100644
--- a/src/runtime.js
+++ b/src/runtime.js
@@ -33,6 +33,8 @@ var GlobalArray = global.Array;
 var GlobalBoolean = global.Boolean;
 var GlobalString = global.String;
 var GlobalNumber = global.Number;
+var isConcatSpreadableSymbol =
+    utils.ImportNow("is_concat_spreadable_symbol");
 
 // ----------------------------------------------------------------------------
 
@@ -765,7 +767,7 @@ function IsPrimitive(x) {
 // ES6, draft 10-14-14, section 22.1.3.1.1
 function IsConcatSpreadable(O) {
   if (!IS_SPEC_OBJECT(O)) return false;
-  var spreadable = O[symbolIsConcatSpreadable];
+  var spreadable = O[isConcatSpreadableSymbol];
   if (IS_UNDEFINED(spreadable)) return IS_ARRAY(O);
   return ToBoolean(spreadable);
 }