Remove more type casts

pkg/analyzer/lib/src/generated/parser.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.parser;
 
 import 'dart:collection';
 import "dart:math" as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1814 matching lines @@
     //
     if (identical(oldNode, originalStructure)) {
       // We ended up re-parsing the whole structure, so there's no need for a
       // copy.
       ResolutionCopier.copyResolutionData(oldNode, newNode);
       return newNode;
     }
     ResolutionCopier.copyResolutionData(oldNode, newNode);
     IncrementalAstCloner cloner =
         new IncrementalAstCloner(oldNode, newNode, _tokenMap);
-    return originalStructure.accept(cloner) as AstNode;
+    return originalStructure.accept(cloner);
   }
 
   /**
    * Return the first (non-EOF) token in the token stream containing the
    * [firstToken].
    */
   Token _findFirstToken(Token firstToken) {
     while (firstToken.type != TokenType.EOF) {
       firstToken = firstToken.previous;
     }
@@ skipping 8126 matching lines @@
    */
   const ParserErrorCode(String name, String message, [String correction])
       : super(name, message, correction);
 
   @override
   ErrorSeverity get errorSeverity => ErrorSeverity.ERROR;
 
   @override
   ErrorType get type => ErrorType.SYNTACTIC_ERROR;
 }