LibWeb: Remove MatchingRule::contains_root_pseudo_class member

This can be a local variable while building a rule cache, no need to
take up space in MatchingRule.

Userland/Libraries/LibWeb/CSS/StyleComputer.cpp

@@ -2699,10 +2699,11 @@ NonnullOwnPtr<StyleComputer::RuleCache> StyleComputer::make_rule_cache_for_casca
                     selector.specificity(),
                     cascade_origin,
                     false,
-                    false,
                     SelectorEngine::can_use_fast_matches(selector),
                 };
 
+                bool contains_root_pseudo_class = false;
+
                 for (auto const& simple_selector : selector.compound_selectors().last().simple_selectors) {
                     if (!matching_rule.contains_pseudo_element) {
                         if (simple_selector.type == CSS::Selector::SimpleSelector::Type::PseudoElement) {
@@ -2710,10 +2711,10 @@ NonnullOwnPtr<StyleComputer::RuleCache> StyleComputer::make_rule_cache_for_casca
                             ++num_pseudo_element_rules;
                         }
                     }
-                    if (!matching_rule.contains_root_pseudo_class) {
+                    if (!contains_root_pseudo_class) {
                         if (simple_selector.type == CSS::Selector::SimpleSelector::Type::PseudoClass
                             && simple_selector.pseudo_class().type == CSS::PseudoClass::Root) {
-                            matching_rule.contains_root_pseudo_class = true;
+                            contains_root_pseudo_class = true;
                             ++num_root_rules;
                         }
                     }
@@ -2752,7 +2753,7 @@ NonnullOwnPtr<StyleComputer::RuleCache> StyleComputer::make_rule_cache_for_casca
                 if (!added_to_bucket) {
                     if (matching_rule.contains_pseudo_element) {
                         rule_cache->pseudo_element_rules.append(move(matching_rule));
-                    } else if (matching_rule.contains_root_pseudo_class) {
+                    } else if (contains_root_pseudo_class) {
                         rule_cache->root_rules.append(move(matching_rule));
                     } else {
                         for (auto const& simple_selector : selector.compound_selectors().last().simple_selectors) {

Userland/Libraries/LibWeb/CSS/StyleComputer.h

@@ -91,7 +91,6 @@ struct MatchingRule {
     u32 specificity { 0 };
     CascadeOrigin cascade_origin;
     bool contains_pseudo_element { false };
-    bool contains_root_pseudo_class { false };
     bool can_use_fast_matches { false };
     bool skip { false };
 };