Implement lazy block layout prototype behind a runtime flag.

Source/core/css/CSSParser.cpp

 /*
  * Copyright (C) 2003 Lars Knoll (knoll@kde.org)
  * Copyright (C) 2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2004, 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Nicholas Shanks <webkit@nickshanks.com>
  * Copyright (C) 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (C) 2012 Adobe Systems Incorporated. All rights reserved.
  * Copyright (C) 2012 Intel Corporation. All rights reserved.
  *
@@ skipping 658 matching lines @@
             return true;
         break;
     case CSSPropertyDirection: // ltr | rtl | inherit
         if (valueID == CSSValueLtr || valueID == CSSValueRtl)
             return true;
         break;
     case CSSPropertyDisplay:
         // inline | block | list-item | run-in | inline-block | table |
         // inline-table | table-row-group | table-header-group | table-footer-group | table-row |
         // table-column-group | table-column | table-cell | table-caption | -webkit-box | -webkit-inline-box | none | inherit
-        // -webkit-flex | -webkit-inline-flex | -webkit-grid | -webkit-inline-grid
+        // -webkit-flex | -webkit-inline-flex | -webkit-grid | -webkit-inline-grid | lazy-block
         if ((valueID >= CSSValueInline && valueID <= CSSValueWebkitInlineFlex) || valueID == CSSValueNone)
             return true;
         if (parserContext.isCSSGridLayoutEnabled && (valueID == CSSValueWebkitGrid || valueID == CSSValueWebkitInlineGrid))
             return true;
+        if (valueID == CSSValueLazyBlock)
+            return RuntimeEnabledFeatures::lazyLayoutEnabled();
         break;
 
     case CSSPropertyEmptyCells: // show | hide | inherit
         if (valueID == CSSValueShow || valueID == CSSValueHide)
             return true;
         break;
     case CSSPropertyFloat: // left | right | none | center (for buggy CSS, maps to none)
         if (valueID == CSSValueLeft || valueID == CSSValueRight || valueID == CSSValueNone || valueID == CSSValueCenter)
             return true;
         break;
@@ skipping 11027 matching lines @@
 {
     // The tokenizer checks for the construct of an+b.
     // However, since the {ident} rule precedes the {nth} rule, some of those
     // tokens are identified as string literal. Furthermore we need to accept
     // "odd" and "even" which does not match to an+b.
     return equalIgnoringCase(token, "odd") || equalIgnoringCase(token, "even")
         || equalIgnoringCase(token, "n") || equalIgnoringCase(token, "-n");
 }
 
 }