Remove ExecutableElement.labels altogether.

pkg/analyzer/lib/src/fasta/mock_element.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.
 
 library fasta.analyzer.mock_element;
 
 import 'package:analyzer/dart/ast/ast.dart';
 import 'package:analyzer/dart/element/element.dart';
 import 'package:analyzer/dart/element/type.dart';
 import 'package:analyzer/src/generated/source.dart';
@@ skipping 123 matching lines @@
 
   bool get isGenerator => internalError("not supported.");
 
   bool get isOperator => internalError("not supported.");
 
   @override
   bool get isStatic => internalError("not supported.");
 
   bool get isSynchronous => internalError("not supported.");
 
-  List<LabelElement> get labels => internalError("not supported.");
-
   @override
   get visibleRange => internalError("not supported.");
 
   bool get hasImplicitType => internalError("not supported.");
 
   FunctionElement get initializer => internalError("not supported.");
 
   @override
   bool get isConst => internalError("not supported.");
 
@@ skipping 337 matching lines @@
   computeConstantValue() => internalError("not supported.");
 
   @override
   void appendToWithoutDelimiters(StringBuffer buffer) {
     return internalError("not supported.");
   }
 
   @override
   FormalParameter computeNode() => internalError("not supported.");
 }