Implement lazy block layout prototype behind a runtime flag.

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 1238 matching lines @@
             break;
         case INLINE_FLEX:
             m_value.ident = CSSValueWebkitInlineFlex;
             break;
         case GRID:
             m_value.ident = CSSValueWebkitGrid;
             break;
         case INLINE_GRID:
             m_value.ident = CSSValueWebkitInlineGrid;
             break;
+        case LAZY_BLOCK:
+            m_value.ident = CSSValueLazyBlock;
+            break;
         case NONE:
             m_value.ident = CSSValueNone;
             break;
     }
 }
 
 template<> inline CSSPrimitiveValue::operator EDisplay() const
 {
     if (m_value.ident == CSSValueNone)
         return NONE;
@@ skipping 3317 matching lines @@
 
     ASSERT_NOT_REACHED();
     return OriginTopLeft;
 }
 
 #endif // ENABLE(CSS_IMAGE_ORIENTATION)
 
 }
 
 #endif