fix #25578, implement @covariant parameter overrides

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

 // Copyright (c) 2014, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 library analyzer.src.generated.element_resolver;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/token.dart';
@@ skipping 401 matching lines @@
       // TODO(brianwilkerson) Figure out whether the element can ever be
       // something other than an ExportElement
       _resolveCombinators(exportElement.exportedLibrary, node.combinators);
       resolveMetadata(node);
     }
     return null;
   }
 
   @override
   Object visitFieldFormalParameter(FieldFormalParameter node) {
-    _resolveMetadataForParameter(node.element, node);
+    _resolveMetadataForParameter(node);
     return super.visitFieldFormalParameter(node);
   }
 
   @override
   Object visitFunctionDeclaration(FunctionDeclaration node) {
     resolveMetadata(node);
     return null;
   }
 
   @override
@@ skipping 23 matching lines @@
   }
 
   @override
   Object visitFunctionTypeAlias(FunctionTypeAlias node) {
     resolveMetadata(node);
     return null;
   }
 
   @override
   Object visitFunctionTypedFormalParameter(FunctionTypedFormalParameter node) {
-    _resolveMetadataForParameter(node.element, node);
+    _resolveMetadataForParameter(node);
     return null;
   }
 
   @override
   Object visitImportDirective(ImportDirective node) {
     SimpleIdentifier prefixNode = node.prefix;
     if (prefixNode != null) {
       String prefixName = prefixNode.name;
       List<PrefixElement> prefixes = _definingLibrary.prefixes;
       int count = prefixes.length;
@@ skipping 571 matching lines @@
     List<ParameterElement> parameters =
         _resolveArgumentsToFunction(false, argumentList, element);
     if (parameters != null) {
       argumentList.correspondingStaticParameters = parameters;
     }
     return null;
   }
 
   @override
   Object visitSimpleFormalParameter(SimpleFormalParameter node) {
-    _resolveMetadataForParameter(node.element, node);
+    _resolveMetadataForParameter(node);
     return null;
   }
 
   @override
   Object visitSimpleIdentifier(SimpleIdentifier node) {
     //
     // Synthetic identifiers have been already reported during parsing.
     //
     if (node.isSynthetic) {
       return null;
@@ skipping 1194 matching lines @@
       }
     }
     // TODO(brianwilkerson) Report this error.
     return null;
   }
 
   /**
    * Given a [node] that can have annotations associated with it, resolve the
    * annotations in the element model representing annotations to the node.
    */
-  void _resolveMetadataForParameter(
-      Element element, NormalFormalParameter node) {
+  void _resolveMetadataForParameter(NormalFormalParameter node) {
     _resolveAnnotations(node.metadata);
   }
 
   /**
    * Given that we are accessing a property of the given [targetType] with the
    * given [propertyName], return the element that represents the property. The
    * [target] is the target of the invocation ('e').
    */
   ExecutableElement _resolveProperty(
       Expression target, DartType targetType, SimpleIdentifier propertyName) {
@@ skipping 351 matching lines @@
 
   @override
   Element get staticElement => null;
 
   @override
   dynamic/*=E*/ accept/*<E>*/(AstVisitor/*<E>*/ visitor) => null;
 
   @override
   void visitChildren(AstVisitor visitor) {}
 }