Adding PreRole in blink side to expose HTML pre tag with correct MSAA+IA2.

public/web/WebAXEnums.h

 /*
  * Copyright (C) 2013 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 133 matching lines @@
     WebAXRoleMenuListOption,
     WebAXRoleMenuListPopup,
     WebAXRoleMenu,
     WebAXRoleMeter,
     WebAXRoleNavigation,
     WebAXRoleNone,
     WebAXRoleNote,
     WebAXRoleOutline,
     WebAXRoleParagraph,
     WebAXRolePopUpButton,
+    WebAXRolePre,
     WebAXRolePresentational,
     WebAXRoleProgressIndicator,
     WebAXRoleRadioButton,
     WebAXRoleRadioGroup,
     WebAXRoleRegion,
     WebAXRoleRootWebArea,
     WebAXRoleRowHeader,
     WebAXRoleRow,
     WebAXRoleRulerMarker,
     WebAXRoleRuler,
@@ skipping 64 matching lines @@
 enum WebAXTextDirection {
     WebAXTextDirectionLR,
     WebAXTextDirectionRL,
     WebAXTextDirectionTB,
     WebAXTextDirectionBT
 };
 
 } // namespace blink
 
 #endif