Enable map transitions for accessor properties.

src/regexp.js

 // Copyright 2012 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 409 matching lines @@
   // value is set the value it is set to is coerced to a string.
   // Getter and setter for the input.
   var RegExpGetInput = function() {
     var regExpInput = LAST_INPUT(lastMatchInfo);
     return IS_UNDEFINED(regExpInput) ? "" : regExpInput;
   };
   var RegExpSetInput = function(string) {
     LAST_INPUT(lastMatchInfo) = ToString(string);
   };
 
+  %OptimizeObjectForAddingMultipleProperties($RegExp, 22);
   %DefineOrRedefineAccessorProperty($RegExp, 'input', RegExpGetInput,
                                     RegExpSetInput, DONT_DELETE);
   %DefineOrRedefineAccessorProperty($RegExp, '$_', RegExpGetInput,
                                     RegExpSetInput, DONT_ENUM | DONT_DELETE);
   %DefineOrRedefineAccessorProperty($RegExp, '$input', RegExpGetInput,
                                     RegExpSetInput, DONT_ENUM | DONT_DELETE);
 
   // The properties multiline and $* are aliases for each other.  When this
   // value is set in SpiderMonkey, the value it is set to is coerced to a
   // boolean.  We mimic that behavior with a slight difference: in SpiderMonkey
@@ skipping 34 matching lines @@
                                     RegExpGetRightContext, NoOpSetter,
                                     DONT_DELETE);
   %DefineOrRedefineAccessorProperty($RegExp, "$'", RegExpGetRightContext,
                                     NoOpSetter, DONT_ENUM | DONT_DELETE);
 
   for (var i = 1; i < 10; ++i) {
     %DefineOrRedefineAccessorProperty($RegExp, '$' + i,
                                       RegExpMakeCaptureGetter(i), NoOpSetter,
                                       DONT_DELETE);
   }
+  %ToFastProperties($RegExp);
 }
 
 SetUpRegExp();