[selectors4] Implement :focus-within pseudo-class

third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp

Index: third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
diff --git a/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp b/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
index 65a3dd89aae153dda07d0928f2ea9298a2891c0d..7eaa8ae1c7de0249c51e917b653cd187f5c1fab9 100644
--- a/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
+++ b/third_party/WebKit/Source/core/css/parser/CSSSelectorParser.cpp
@@ -173,6 +173,7 @@ bool IsUserActionPseudoClass(CSSSelector::PseudoType pseudo) {
   switch (pseudo) {
     case CSSSelector::kPseudoHover:
     case CSSSelector::kPseudoFocus:
+    case CSSSelector::kPseudoFocusWithin:
     case CSSSelector::kPseudoActive:
       return true;
     default:
@@ -443,6 +444,10 @@ std::unique_ptr<CSSParserSelector> CSSSelectorParser::ConsumePseudo(
   bool has_arguments = token.GetType() == kFunctionToken;
   selector->UpdatePseudoType(value, has_arguments);
 
+  if (!RuntimeEnabledFeatures::cssSelectorsFocusWithinEnabled() &&
+      selector->GetPseudoType() == CSSSelector::kPseudoFocusWithin)
+    return nullptr;
+
   if (selector->Match() == CSSSelector::kPseudoElement &&
       disallow_pseudo_elements_)
     return nullptr;