Move background related longhands into CSSPropertyParser

third_party/WebKit/Source/core/css/CSSGradientValue.cpp

 /*
  * Copyright (C) 2008 Apple Inc.  All rights reserved.
  * Copyright (C) 2015 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:
  * 1. Redistributions of source code must retain the above copyright
  *    notice, this list of conditions and the following disclaimer.
  * 2. Redistributions in binary form must reproduce the above copyright
@@ skipping 506 matching lines @@
         return 0;
     case CSSValueLeft:
         ASSERT(isHorizontal);
         return 0;
     case CSSValueBottom:
         ASSERT(!isHorizontal);
         return size.height();
     case CSSValueRight:
         ASSERT(isHorizontal);
         return size.width();
+    case CSSValueCenter:
+        return origin + sign * .5f * edgeDistance;
     default:
         break;
     }
 
     return origin + sign * primitiveValue->computeLength<float>(conversionData);
 }
 
 FloatPoint CSSGradientValue::computeEndPoint(CSSValue* horizontal, CSSValue* vertical, const CSSToLengthConversionData& conversionData, const IntSize& size)
 {
     FloatPoint result;
@@ skipping 681 matching lines @@
     visitor->trace(m_firstRadius);
     visitor->trace(m_secondRadius);
     visitor->trace(m_shape);
     visitor->trace(m_sizingBehavior);
     visitor->trace(m_endHorizontalSize);
     visitor->trace(m_endVerticalSize);
     CSSGradientValue::traceAfterDispatch(visitor);
 }
 
 } // namespace blink