Implement select listbox using shadow DOM

Source/core/css/SelectorChecker.cpp

Index: Source/core/css/SelectorChecker.cpp
diff --git a/Source/core/css/SelectorChecker.cpp b/Source/core/css/SelectorChecker.cpp
index c595be7027949db417ffc730fa556921431a3739..6f66f385a12e86832edf8951eae8a77d334848c8 100644
--- a/Source/core/css/SelectorChecker.cpp
+++ b/Source/core/css/SelectorChecker.cpp
@@ -950,6 +950,8 @@ bool SelectorChecker::checkOne(const SelectorCheckingContext& context, const Sib
                 }
             }
             break;
+        case CSSSelector::PseudoSpatialNavigationFocus:
+            return context.isUARule && matchesSpatialNavigationFocusPseudoClass(element);
 
         case CSSSelector::PseudoHorizontal:
         case CSSSelector::PseudoVertical:
@@ -1122,6 +1124,11 @@ bool SelectorChecker::matchesFocusPseudoClass(const Element& element)
     return element.focused() && isFrameFocused(element);
 }
 
+bool SelectorChecker::matchesSpatialNavigationFocusPseudoClass(const Element& element)
+{
+    return isHTMLOptionElement(element) && toHTMLOptionElement(element).spatialNavigationFocused() && isFrameFocused(element);
+}
+
 template
 SelectorChecker::Match SelectorChecker::match(const SelectorCheckingContext&, const DOMSiblingTraversalStrategy&, MatchResult*) const;