Implement unset value handling

Source/core/css/resolver/StyleResolver.cpp

Index: Source/core/css/resolver/StyleResolver.cpp
diff --git a/Source/core/css/resolver/StyleResolver.cpp b/Source/core/css/resolver/StyleResolver.cpp
index 1d39ce659c8397fab8cfaae8213e400f299e4443..2125d545b93fdfa362c9a7f4408efce3cfb87e42 100644
--- a/Source/core/css/resolver/StyleResolver.cpp
+++ b/Source/core/css/resolver/StyleResolver.cpp
@@ -1367,6 +1367,14 @@ void StyleResolver::applyProperties(StyleResolverState& state, const StyleProper
         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());
     }
 }