Remove support of nonstandard 'CSSValueCenter' property value for floated element.

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 1405 matching lines @@
 
 template<> inline CSSPrimitiveValue::operator EFloat() const
 {
     ASSERT(isValueID());
     switch (m_value.valueID) {
     case CSSValueLeft:
         return LeftFloat;
     case CSSValueRight:
         return RightFloat;
     case CSSValueNone:
-    case CSSValueCenter: // Non-standard CSS value.
         return NoFloat;
     default:
         break;
     }
 
     ASSERT_NOT_REACHED();
     return NoFloat;
 }
 
 template<> inline CSSPrimitiveValue::CSSPrimitiveValue(LineBreak e)
@@ skipping 3265 matching lines @@
     default:
         break;
     }
     ASSERT_NOT_REACHED();
     return ScrollBehaviorAuto;
 }
 
 }
 
 #endif