[CSS Grid Layout] Add support to place items using named grid lines

Source/core/css/resolver/StyleBuilderCustom.cpp

 /*
  * Copyright (C) 2013 Google Inc. All rights reserved.
  * Copyright (C) 1999 Lars Knoll (knoll@kde.org)
  *           (C) 2004-2005 Allan Sandfeld Jensen (kde@carewolf.com)
  * Copyright (C) 2006, 2007 Nicholas Shanks (webkit@nickshanks.com)
  * Copyright (C) 2005, 2006, 2007, 2008, 2009, 2010, 2011, 2012, 2013 Apple Inc. All rights reserved.
  * Copyright (C) 2007 Alexey Proskuryakov <ap@webkit.org>
  * Copyright (C) 2007, 2008 Eric Seidel <eric@webkit.org>
  * Copyright (C) 2008, 2009 Torch Mobile Inc. All rights reserved. (http://www.torchmobile.com/)
  * Copyright (c) 2011, Code Aurora Forum. All rights reserved.
@@ skipping 986 matching lines @@
 static bool createGridPosition(CSSValue* value, GridPosition& position)
 {
     // We accept the specification's grammar:
     // 'auto' | [ <integer> || <string> ] | [ span && [ <integer> || string ] ] | <ident>
 
     if (value->isPrimitiveValue()) {
         CSSPrimitiveValue* primitiveValue = toCSSPrimitiveValue(value);
         // We translate <ident> to <string> during parsing as it
         // makes handling it more simple.
         if (primitiveValue->isString()) {
+            // Note that a <ident> could be either a grid area or a grid line name. We create them as grid areas but the
+            // StyleAdjuster will have to check if this is the name of a grid area, the name of a grid line or the
+            // prefix of a grid line named <ident>-start or <ident>-end.
             position.setNamedGridArea(primitiveValue->getStringValue());
             return true;
         }
 
         ASSERT(primitiveValue->getValueID() == CSSValueAuto);
         return true;
     }
 
     CSSValueList* values = toCSSValueList(value);
     ASSERT(values->length());
@@ skipping 1154 matching lines @@
         break;
     }
     case CSSPropertyEnableBackground:
         // Silently ignoring this property for now
         // http://bugs.webkit.org/show_bug.cgi?id=6022
         break;
     }
 }
 
 } // namespace WebCore