style: Clear last_parsed_property_id right after successfully parsing…

… the value.

Rather than waiting until parsing another id (successfully or
unsuccessfully).

If we error before we even get to PropertyId::parse, we'd incorrectly
associate the error with the wrong property, incorrectly omitting it
sometimes.

Differential Revision: https://phabricator.services.mozilla.com/D78260

components/style/properties/declaration_block.rs

@@ -1347,7 +1347,6 @@ impl<'a, 'b, 'i> DeclarationParser<'i> for PropertyDeclarationParser<'a, 'b> {
         let id = match PropertyId::parse(&name, self.context) {
             Ok(id) => id,
             Err(..) => {
-                self.last_parsed_property_id = None;
                 return Err(input.new_custom_error(StyleParseErrorKind::UnknownProperty(name)));
             },
         };
@@ -1469,6 +1468,10 @@ pub fn parse_property_declaration_list(
         match declaration {
             Ok(importance) => {
                 block.extend(iter.parser.declarations.drain(), importance);
+                // We've successfully parsed a declaration, so forget about
+                // `last_parsed_property_id`. It'd be wrong to associate any
+                // following error with this property.
+                iter.parser.last_parsed_property_id = None;
             },
             Err((error, slice)) => {
                 iter.parser.declarations.clear();