Rollup merge of #16993 - emilio:moz-placeholder, r=heycam

stylo: Parse but never match :-moz-placeholder as a pseudo-class.

Fixes bug 1366709.

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components/style/gecko/non_ts_pseudo_class_list.rs

@@ -107,6 +107,7 @@ macro_rules! apply_non_ts_list {
                 ("-moz-only-whitespace", MozOnlyWhitespace, mozOnlyWhitespace, _, _),
                 ("-moz-native-anonymous", MozNativeAnonymous, mozNativeAnonymous, _, PSEUDO_CLASS_INTERNAL),
                 ("-moz-is-html", MozIsHTML, mozIsHTML, _, _),
+                ("-moz-placeholder", MozPlaceholder, mozPlaceholder, _, _),
             ],
             string: [
                 ("-moz-system-metric", MozSystemMetric, mozSystemMetric, _, PSEUDO_CLASS_INTERNAL),

components/style/gecko/selector_parser.rs

@@ -166,7 +166,8 @@ impl NonTSPseudoClass {
         !matches!(*self,
                   NonTSPseudoClass::MozAny(_) |
                   NonTSPseudoClass::Dir(_) |
-                  NonTSPseudoClass::MozIsHTML)
+                  NonTSPseudoClass::MozIsHTML |
+                  NonTSPseudoClass::MozPlaceholder)
     }
 
     /// Convert NonTSPseudoClass to Gecko's CSSPseudoClassType.

components/style/gecko/wrapper.rs

@@ -1335,6 +1335,7 @@ impl<'le> ::selectors::Element for GeckoElement<'le> {
             NonTSPseudoClass::MozIsHTML => {
                 self.is_html_element_in_html_document()
             }
+            NonTSPseudoClass::MozPlaceholder => false,
             NonTSPseudoClass::MozAny(ref sels) => {
                 sels.iter().any(|s| {
                     matches_complex_selector(s, self, context, flags_setter)