Avoid calling overwritten toString methods for internal error

src/messages.js

 // Copyright 2006-2008 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 72 matching lines @@
   for (var i = 0; i < args.length; i++) {
     var str;
     try { str = ToDetailString(args[i]); }
     catch (e) { str = "#<error>"; }
     result = ArrayJoin.call(StringSplit.call(result, "%" + i), str);
   }
   return result;
 }
 
 
+// When formatting internally created error messages, do not
+// invoke overwritten error toString methods but explicitly use
+// the error to string method. This is to avoid leaking error
+// objects between script tags in a browser setting.
+function ToStringCheckErrorObject(obj) {
+  if (obj instanceof $Error) {
+    return %_CallFunction(obj, errorToString);
+  } else {
+    return ToString(obj);
+  }
+}
+
+
 function ToDetailString(obj) {
   if (obj != null && IS_OBJECT(obj) && obj.toString === $Object.prototype.toString) {
     var constructor = obj.constructor;
-    if (!constructor) return ToString(obj);
+    if (!constructor) return ToStringCheckErrorObject(obj);
     var constructorName = constructor.name;
-    if (!constructorName) return ToString(obj);
+    if (!constructorName) return ToStringCheckErrorObject(obj);
     return "#<" + GetInstanceName(constructorName) + ">";
-  } else if (obj instanceof $Error) {
-    // When formatting internally created error messages, do not
-    // invoke overwritten error toString methods but explicitly use
-    // the error to string method. This is to avoid leaking error
-    // objects between script tags in a browser setting.
-    return %_CallFunction(obj, errorToString);
   } else {
-    return ToString(obj);
+    return ToStringCheckErrorObject(obj);
   }
 }
 
 
 function MakeGenericError(constructor, type, args) {
   if (IS_UNDEFINED(args)) {
     args = [];
   }
   var e = new constructor(kAddMessageAccessorsMarker);
   e.type = type;
@@ skipping 928 matching lines @@
     else throw e;
   }
 }
 
 %FunctionSetName(errorToString, 'toString');
 %SetProperty($Error.prototype, 'toString', errorToString, DONT_ENUM);
 
 // Boilerplate for exceptions for stack overflows. Used from
 // Top::StackOverflow().
 const kStackOverflowBoilerplate = MakeRangeError('stack_overflow', []);