[CSS Grid Layout] Remove stack from grid-auto-flow syntax

Source/core/css/RenderStyleCSSValueMapping.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 1555 matching lines @@
         RefPtrWillBeRawPtr<CSSValueList> list = CSSValueList::createSpaceSeparated();
         switch (style.gridAutoFlow()) {
         case AutoFlowRow:
         case AutoFlowRowDense:
             list->append(cssValuePool().createIdentifierValue(CSSValueRow));
             break;
         case AutoFlowColumn:
         case AutoFlowColumnDense:
             list->append(cssValuePool().createIdentifierValue(CSSValueColumn));
             break;
-        case AutoFlowStackRow:
-        case AutoFlowStackColumn:
-            list->append(cssValuePool().createIdentifierValue(CSSValueStack));
-            break;
         default:
             ASSERT_NOT_REACHED();
         }
 
         switch (style.gridAutoFlow()) {
         case AutoFlowRowDense:
         case AutoFlowColumnDense:
             list->append(cssValuePool().createIdentifierValue(CSSValueDense));
             break;
-        case AutoFlowStackRow:
-            list->append(cssValuePool().createIdentifierValue(CSSValueRow));
-            break;
-        case AutoFlowStackColumn:
-            list->append(cssValuePool().createIdentifierValue(CSSValueColumn));
-            break;
         default:
             // Do nothing.
             break;
         }
 
         return list.release();
     }
     // Specs mention that getComputedStyle() should return the used value of the property instead of the computed
     // one for grid-definition-{rows|columns} but not for the grid-auto-{rows|columns} as things like
     // grid-auto-columns: 2fr; cannot be resolved to a value in pixels as the '2fr' means very different things
@@ skipping 952 matching lines @@
         return nullptr;
 
     case CSSPropertyAll:
         return nullptr;
     }
     ASSERT_NOT_REACHED();
     return nullptr;
 }
 
 }