Remove -webkit-appearance:default-button. This was only used in Safari.

Source/core/css/CSSPrimitiveValueMappings.h

 /*
  * Copyright (C) 2007 Alexey Proskuryakov <ap@nypop.com>.
  * Copyright (C) 2008, 2009, 2010, 2011 Apple Inc. All rights reserved.
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2009 Jeff Schiller <codedread@gmail.com>
  * Copyright (C) Research In Motion Limited 2010. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
  * are met:
@@ skipping 383 matching lines @@
             break;
         case SquareButtonPart:
             m_value.ident = CSSValueSquareButton;
             break;
         case ButtonPart:
             m_value.ident = CSSValueButton;
             break;
         case ButtonBevelPart:
             m_value.ident = CSSValueButtonBevel;
             break;
-        case DefaultButtonPart:
-            m_value.ident = CSSValueDefaultButton;
-            break;
         case InnerSpinButtonPart:
             m_value.ident = CSSValueInnerSpinButton;
             break;
         case ListboxPart:
             m_value.ident = CSSValueListbox;
             break;
         case ListItemPart:
             m_value.ident = CSSValueListitem;
             break;
         case MediaEnterFullscreenButtonPart:
@@ skipping 4169 matching lines @@
 
     ASSERT_NOT_REACHED();
     return OriginTopLeft;
 }
 
 #endif // ENABLE(CSS_IMAGE_ORIENTATION)
 
 }
 
 #endif