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

Source/core/rendering/RenderThemeChromiumMac.mm

 /*
  * Copyright (C) 2005, 2006, 2007, 2008, 2009 Apple Inc. All rights reserved.
  * Copyright (C) 2008, 2009 Google, Inc.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Library General Public
  * License as published by the Free Software Foundation; either
  * version 2 of the License, or (at your option) any later version.
  *
  * This library is distributed in the hope that it will be useful,
@@ skipping 508 matching lines @@
 void RenderThemeChromiumMac::adjustRepaintRect(const RenderObject* o, IntRect& r)
 {
     ControlPart part = o->style()->appearance();
 
 #if USE(NEW_THEME)
     switch (part) {
         case CheckboxPart:
         case RadioPart:
         case PushButtonPart:
         case SquareButtonPart:
-        case DefaultButtonPart:
         case ButtonPart:
         case InnerSpinButtonPart:
             return RenderTheme::adjustRepaintRect(o, r);
         default:
             break;
     }
 #endif
 
     float zoomLevel = o->style()->effectiveZoom();
 
@@ skipping 1435 matching lines @@
 {
     return RenderMediaControlsChromium::paintMediaControlsPart(MediaEnterFullscreenButton, object, paintInfo, rect);
 }
 
 bool RenderThemeChromiumMac::paintMediaToggleClosedCaptionsButton(RenderObject* object, const PaintInfo& paintInfo, const IntRect& rect)
 {
     return RenderMediaControlsChromium::paintMediaControlsPart(MediaShowClosedCaptionsButton, object, paintInfo, rect);
 }
 
 } // namespace WebCore