Implement unset value handling

Source/core/css/resolver/StyleResolver.cpp

 /*
  * 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.
  * Copyright (C) Research In Motion Limited 2011. All rights reserved.
@@ skipping 1349 matching lines @@
             // If the property value is explicitly inherited, we need to apply further non-inherited properties
             // as they might override the value inherited here. For this reason we don't allow declarations with
             // explicitly inherited properties to be cached.
             ASSERT(!current.value()->isInheritedValue());
             continue;
         }
 
         if (!isPropertyForPass<pass>(property))
             continue;
 
+        if (current.value()->isUnsetValue()) {
+            if (CSSPropertyMetadata::isInheritedProperty(property))
+                StyleBuilder::applyProperty(property, state, cssValuePool().createInheritedValue().get());
+            else
+                StyleBuilder::applyProperty(property, state, cssValuePool().createExplicitInitialValue().get());
+            continue;
+        }
+
         StyleBuilder::applyProperty(current.id(), state, current.value());
     }
 }
 
 template <StyleResolver::StyleApplicationPass pass>
 void StyleResolver::applyMatchedProperties(StyleResolverState& state, const MatchResult& matchResult, bool isImportant, int startIndex, int endIndex, bool inheritedOnly)
 {
     if (startIndex == -1)
         return;
 
@@ skipping 226 matching lines @@
     visitor->trace(m_uncommonAttributeRuleSet);
     visitor->trace(m_watchedSelectorsRules);
     visitor->trace(m_treeBoundaryCrossingRules);
     visitor->trace(m_styleSharingLists);
     visitor->trace(m_pendingStyleSheets);
     visitor->trace(m_document);
 #endif
 }
 
 } // namespace blink