Limit HTMLKeygenElement.keytype to only known values.

Source/core/html/HTMLKeygenElement.idl

 /*
  * Copyright (C) 2011 Google Inc. 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
@@ skipping 15 matching lines @@
  * THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT
  * (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE USE
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE.
  */
 
 interface HTMLKeygenElement : HTMLElement {
     [Reflect] attribute boolean autofocus;
     [Reflect] attribute DOMString challenge;
     [Reflect] attribute boolean disabled;
     [ImplementedAs=formOwner] readonly attribute HTMLFormElement form;
-    [Reflect] attribute DOMString keytype;
+    [Reflect, ReflectOnly=rsa] attribute DOMString keytype;
     [Reflect] attribute DOMString name;
 
     readonly attribute DOMString type;
 
     readonly attribute boolean willValidate;
     readonly attribute ValidityState validity;
     readonly attribute DOMString validationMessage;
     boolean checkValidity();
     void setCustomValidity([TreatNullAs=NullString, TreatUndefinedAs=NullString] DOMString error);
 
     readonly attribute NodeList labels;
 };