Use "Object" as the reified type of covariant override parameters.

pkg/analyzer/lib/src/dart/element/member.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.dart.element.member;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/constant/value.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
@@ skipping 585 matching lines @@
   ClassElement get enclosingElement => baseElement.enclosingElement;
 
   @override
   /*=T*/ accept/*<T>*/(ElementVisitor<dynamic/*=T*/ > visitor) =>
       visitor.visitMethodElement(this);
 
   @override
   MethodDeclaration computeNode() => baseElement.computeNode();
 
   @override
+  FunctionType getReifiedType(DartType objectType) =>
+      baseElement.getReifiedType(objectType);
+
+  @override
   String toString() {
     MethodElement baseElement = this.baseElement;
     List<ParameterElement> parameters = this.parameters;
     FunctionType type = this.type;
     StringBuffer buffer = new StringBuffer();
     buffer.write(baseElement.enclosingElement.displayName);
     buffer.write(".");
     buffer.write(baseElement.displayName);
     buffer.write("(");
     int parameterCount = parameters.length;
@@ skipping 406 matching lines @@
   DartObject computeConstantValue() => baseElement.computeConstantValue();
 
   @override
   void visitChildren(ElementVisitor visitor) {
     // TODO(brianwilkerson) We need to finish implementing the accessors used
     // below so that we can safely invoke them.
     super.visitChildren(visitor);
     baseElement.initializer?.accept(visitor);
   }
 }