Fix regression in JSON serialization of RegExps.

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 172 matching lines @@
       stack_overflow:               "Maximum call stack size exceeded",
       // SyntaxError
       unable_to_parse:              "Parse error",
       duplicate_regexp_flag:        "Duplicate RegExp flag %0",
       invalid_regexp:               "Invalid RegExp pattern /%0/",
       illegal_break:                "Illegal break statement",
       illegal_continue:             "Illegal continue statement",
       illegal_return:               "Illegal return statement",
       error_loading_debugger:       "Error loading debugger",
       no_input_to_regexp:           "No input to %0",
-      result_not_primitive:         "Result of %0 must be a primitive, was %1",
       invalid_json:                 "String '%0' is not valid JSON",
       circular_structure:           "Converting circular structure to JSON",
       obj_ctor_property_non_object: "Object.%0 called on non-object",
       array_indexof_not_defined:    "Array.getIndexOf: Argument undefined",
       object_not_extensible:        "Can't add property %0, object is not extensible",
       illegal_access:               "Illegal access",
       invalid_preparser_data:       "Invalid preparser data for function %0"
     };
   }
   var format = kMessages[message.type];
@@ skipping 790 matching lines @@
     return this.name + ": " + FormatMessage({ type: type, args: this.arguments });
   }
   var message = this.message;
   return this.name + (message ? (": " + message) : "");
 }, DONT_ENUM);
 
 
 // Boilerplate for exceptions for stack overflows. Used from
 // Top::StackOverflow().
 const kStackOverflowBoilerplate = MakeRangeError('stack_overflow', []);