When DefaultFormalParameter, don't use ParameterKind.REQUIRED.

pkg/analyzer/lib/src/generated/parser.dart

Index: pkg/analyzer/lib/src/generated/parser.dart
diff --git a/pkg/analyzer/lib/src/generated/parser.dart b/pkg/analyzer/lib/src/generated/parser.dart
index 4430e76a7148572e28e47b0742553acf384c1bdf..e325da2e537b216f1974ea5428c4e587d60efe76 100644
--- a/pkg/analyzer/lib/src/generated/parser.dart
+++ b/pkg/analyzer/lib/src/generated/parser.dart
@@ -2799,6 +2799,7 @@ class Parser {
       if (kind == ParameterKind.REQUIRED) {
         _reportErrorForNode(
             ParserErrorCode.POSITIONAL_PARAMETER_OUTSIDE_GROUP, parameter);
+        kind = ParameterKind.POSITIONAL;
       }
       return new DefaultFormalParameter(
           parameter, kind, separator, defaultValue);
@@ -2812,6 +2813,7 @@ class Parser {
       } else if (kind == ParameterKind.REQUIRED) {
         _reportErrorForNode(
             ParserErrorCode.NAMED_PARAMETER_OUTSIDE_GROUP, parameter);
+        kind = ParameterKind.NAMED;
       }
       return new DefaultFormalParameter(
           parameter, kind, separator, defaultValue);