Deprecate enable-background property

Source/core/css/ComputedStyleCSSValueMapping.cpp

 /*
  * Copyright (C) 2004 Zack Rusin <zack@kde.org>
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2011 Sencha, Inc. All rights reserved.
  * Copyright (C) 2015 Google Inc. All rights reserved.
  *
  * This library is free software; you can redistribute it and/or
  * modify it under the terms of the GNU Lesser General Public
@@ skipping 2611 matching lines @@
             return CSSPrimitiveValue::createIdentifier(CSSValueAuto);
         return nullptr;
     }
     case CSSPropertyPaintOrder:
         return paintOrderToCSSValueList(svgStyle);
     case CSSPropertyVectorEffect:
         return CSSPrimitiveValue::create(svgStyle.vectorEffect());
     case CSSPropertyMaskType:
         return CSSPrimitiveValue::create(svgStyle.maskType());
     case CSSPropertyMarker:
-    case CSSPropertyEnableBackground:
         // the above properties are not yet implemented in the engine
         return nullptr;
     case CSSPropertyCx:
         return zoomAdjustedPixelValueForLength(svgStyle.cx(), style);
     case CSSPropertyCy:
         return zoomAdjustedPixelValueForLength(svgStyle.cy(), style);
     case CSSPropertyX:
         return zoomAdjustedPixelValueForLength(svgStyle.x(), style);
     case CSSPropertyY:
         return zoomAdjustedPixelValueForLength(svgStyle.y(), style);
@@ skipping 66 matching lines @@
     case CSSPropertyAll:
         return nullptr;
     default:
         break;
     }
     ASSERT_NOT_REACHED();
     return nullptr;
 }
 
 }