Add missing AST support for covariant keyword and fix bug from previous CL

pkg/analyzer/lib/src/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.
 
 library analyzer.src.dart.ast.ast;
 
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/ast/syntactic_entity.dart';
@@ skipping 4304 matching lines @@
 }
 
 /**
  * The declaration of one or more fields of the same type.
  *
  *    fieldDeclaration ::=
  *        'static'? [VariableDeclarationList] ';'
  */
 class FieldDeclarationImpl extends ClassMemberImpl implements FieldDeclaration {
   /**
+   * The 'covariant' keyword, or `null` if the keyword was not used.
+   */
+  Token covariantKeyword;
+
+  /**
    * The token representing the 'static' keyword, or `null` if the fields are
    * not static.
    */
   @override
   Token staticKeyword;
 
   /**
    * The fields being declared.
    */
   VariableDeclarationList _fieldList;
@@ skipping 29 matching lines @@
   @override
   VariableDeclarationList get fields => _fieldList;
 
   @override
   void set fields(VariableDeclarationList fields) {
     _fieldList = _becomeParentOf(fields as AstNodeImpl);
   }
 
   @override
   Token get firstTokenAfterCommentAndMetadata {
-    if (staticKeyword != null) {
+    if (covariantKeyword != null) {
+      return covariantKeyword;
+    } else if (staticKeyword != null) {
       return staticKeyword;
     }
     return _fieldList.beginToken;
   }
 
   @override
   bool get isStatic => staticKeyword != null;
 
   @override
   dynamic/*=E*/ accept/*<E>*/(AstVisitor/*<E>*/ visitor) =>
@@ skipping 72 matching lines @@
       TypeParameterListImpl typeParameters,
       FormalParameterListImpl parameters)
       : super(comment, metadata, identifier) {
     _type = _becomeParentOf(type);
     _typeParameters = _becomeParentOf(typeParameters);
     _parameters = _becomeParentOf(parameters);
   }
 
   @override
   Token get beginToken {
-    if (keyword != null) {
+    NodeList<Annotation> metadata = this.metadata;
+    if (!metadata.isEmpty) {
+      return metadata.beginToken;
+    } else if (covariantKeyword != null) {
+      return covariantKeyword;
+    } else if (keyword != null) {
       return keyword;
     } else if (_type != null) {
       return _type.beginToken;
     }
     return thisKeyword;
   }
 
   @override
   Iterable<SyntacticEntity> get childEntities => super._childEntities
     ..add(keyword)
@@ skipping 1089 matching lines @@
       FormalParameterListImpl parameters,
       this.question)
       : super(comment, metadata, identifier) {
     _returnType = _becomeParentOf(returnType);
     _typeParameters = _becomeParentOf(typeParameters);
     _parameters = _becomeParentOf(parameters);
   }
 
   @override
   Token get beginToken {
-    if (_returnType != null) {
+    NodeList<Annotation> metadata = this.metadata;
+    if (!metadata.isEmpty) {
+      return metadata.beginToken;
+    } else if (covariantKeyword != null) {
+      return covariantKeyword;
+    } else if (_returnType != null) {
       return _returnType.beginToken;
     }
     return identifier.beginToken;
   }
 
   @override
   Iterable<SyntacticEntity> get childEntities =>
       super._childEntities..add(_returnType)..add(identifier)..add(parameters);
 
   @override
@@ skipping 3635 matching lines @@
       this.keyword, TypeAnnotationImpl type, SimpleIdentifierImpl identifier)
       : super(comment, metadata, identifier) {
     _type = _becomeParentOf(type);
   }
 
   @override
   Token get beginToken {
     NodeList<Annotation> metadata = this.metadata;
     if (!metadata.isEmpty) {
       return metadata.beginToken;
+    } else if (covariantKeyword != null) {
+      return covariantKeyword;
     } else if (keyword != null) {
       return keyword;
     } else if (_type != null) {
       return _type.beginToken;
     }
     return identifier.beginToken;
   }
 
   @override
   Iterable<SyntacticEntity> get childEntities =>
@@ skipping 2205 matching lines @@
 
   @override
   dynamic/*=E*/ accept/*<E>*/(AstVisitor/*<E>*/ visitor) =>
       visitor.visitYieldStatement(this);
 
   @override
   void visitChildren(AstVisitor visitor) {
     _expression?.accept(visitor);
   }
 }