Ast changes to support the covariant keyword

pkg/analyzer/lib/dart/ast/ast.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.
 
 /**
  * Defines the AST model. The AST (Abstract Syntax Tree) model describes the
  * syntactic (as opposed to semantic) structure of Dart code. The semantic
  * structure of the code is modeled by the
  * [element model](../element/element.dart).
  *
@@ skipping 2973 matching lines @@
  * A node representing a parameter to a function.
  *
  *    formalParameter ::=
  *        [NormalFormalParameter]
  *      | [DefaultFormalParameter]
  *
  * Clients may not extend, implement or mix-in this class.
  */
 abstract class FormalParameter extends AstNode {
   /**
+   * The 'covariant' keyword, or `null` if the keyword was not used.
+   */
+  Token get covariantKeyword;
+
+  /**
    * Return the element representing this parameter, or `null` if this parameter
    * has not been resolved.
    */
   ParameterElement get element;
 
   /**
    * Return the name of the parameter being declared.
    */
   SimpleIdentifier get identifier;
 
@@ skipping 4067 matching lines @@
   /**
    * Return the 'yield' keyword.
    */
   Token get yieldKeyword;
 
   /**
    * Return the 'yield' keyword to the given [token].
    */
   void set yieldKeyword(Token token);
 }