fix #25578, implement @covariant parameter overrides

pkg/analyzer/lib/src/summary/link.dart

 // Copyright (c) 2016, 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.
 
 /**
  * This library is capable of producing linked summaries from unlinked
  * ones (or prelinked ones).  It functions by building a miniature
  * element model to represent the contents of the summaries, and then
  * scanning the element model to gather linked information and adding
  * it to the summary data structures.
@@ skipping 3883 matching lines @@
    * The index of this parameter within [enclosingElement]'s parameter list.
    */
   final int _parameterIndex;
 
   @override
   final ParameterParentElementForLink enclosingElement;
 
   DartType _inferredType;
   DartType _declaredType;
 
+  @override
+  bool inheritsCovariant = false;
+
   ParameterElementForLink(this.enclosingElement, this._unlinkedParam,
       this._typeParameterContext, this.compilationUnit, this._parameterIndex) {
     if (_unlinkedParam.initializer?.bodyExpr != null) {
       _constNode = new ConstParameterNode(this);
     }
   }
 
   @override
   String get displayName => _unlinkedParam.name;
 
   @override
   bool get hasImplicitType =>
       !_unlinkedParam.isFunctionTyped && _unlinkedParam.type == null;
 
   @override
+  bool get isCovariant => false;
+
+  @override
   String get name => _unlinkedParam.name;
 
   @override
   ParameterKind get parameterKind {
     switch (_unlinkedParam.kind) {
       case UnlinkedParamKind.required:
         return ParameterKind.REQUIRED;
       case UnlinkedParamKind.positional:
         return ParameterKind.POSITIONAL;
       case UnlinkedParamKind.named:
@@ skipping 1027 matching lines @@
    * there are no type parameters in scope.
    */
   TypeParameterizedElementMixin get _typeParameterContext;
 
   @override
   noSuchMethod(Invocation invocation) => super.noSuchMethod(invocation);
 
   @override
   String toString() => '$enclosingElement.$name';
 }