Implement the `RegExp.prototype.flags` getter

src/messages.js

 // Copyright 2012 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.
 
 // -------------------------------------------------------------------
 
 var kMessages = {
   // Error
   cyclic_proto:                  ["Cyclic __proto__ value"],
   code_gen_from_strings:         ["%0"],
@@ skipping 34 matching lines @@
   unsupported_super:             ["Unsupported reference to 'super'"],
   non_object_property_load:      ["Cannot read property '", "%0", "' of ", "%1"],
   non_object_property_store:     ["Cannot set property '", "%0", "' of ", "%1"],
   with_expression:               ["%0", " has no properties"],
   illegal_invocation:            ["Illegal invocation"],
   no_setter_in_callback:         ["Cannot set property ", "%0", " of ", "%1", " which has only a getter"],
   apply_non_function:            ["Function.prototype.apply was called on ", "%0", ", which is a ", "%1", " and not a function"],
   apply_wrong_args:              ["Function.prototype.apply: Arguments list has wrong type"],
   toMethod_non_function:         ["Function.prototype.toMethod was called on ", "%0", ", which is a ", "%1", " and not a function"],
   toMethod_non_object:           ["Function.prototype.toMethod: home object ", "%0", " is not an object"],
+  flags_getter_non_object:       ["RegExp.prototype.flags getter called on non-object ", "%0"],
   invalid_in_operator_use:       ["Cannot use 'in' operator to search for '", "%0", "' in ", "%1"],
   instanceof_function_expected:  ["Expecting a function in instanceof check, but got ", "%0"],
   instanceof_nonobject_proto:    ["Function has non-object prototype '", "%0", "' in instanceof check"],
   undefined_or_null_to_object:   ["Cannot convert undefined or null to object"],
   reduce_no_initial:             ["Reduce of empty array with no initial value"],
   getter_must_be_callable:       ["Getter must be a function: ", "%0"],
   setter_must_be_callable:       ["Setter must be a function: ", "%0"],
   value_and_accessor:            ["Invalid property.  A property cannot both have accessors and be writable or have a value, ", "%0"],
   proto_object_or_null:          ["Object prototype may only be an Object or null: ", "%0"],
   property_desc_object:          ["Property description must be an object: ", "%0"],
@@ skipping 1251 matching lines @@
 function SetUpStackOverflowBoilerplate() {
   var boilerplate = MakeRangeError('stack_overflow', []);
 
   %DefineAccessorPropertyUnchecked(
       boilerplate, 'stack', StackTraceGetter, StackTraceSetter, DONT_ENUM);
 
   return boilerplate;
 }
 
 var kStackOverflowBoilerplate = SetUpStackOverflowBoilerplate();