Default trailing comma support to `true` (#26647).

pkg/analyzer/lib/src/generated/engine.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.engine;
 
 import 'dart:async';
 import 'dart:collection';
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 1069 matching lines @@
    * Object, and are allowed to reference `super`.
    */
   bool get enableSuperMixins;
 
   /**
    * Return `true` if timing data should be gathered during execution.
    */
   bool get enableTiming;
 
   /**
-   * Return `true` to enable trailing commas in parameter and argument lists
-   * (sdk#26647).
-   */
-  bool get enableTrailingCommas;
-
-  /**
    * A flag indicating whether finer grained dependencies should be used
    * instead of just source level dependencies.
    *
    * This option is experimental and subject to change.
    */
   bool get finerGrainedInvalidation;
 
   /**
    * Return `true` if errors, warnings and hints should be generated for sources
    * that are implicitly being analyzed. The default value is `true`.
@@ skipping 234 matching lines @@
   AnalysisOptionsImpl.from(AnalysisOptions options) {
     analyzeFunctionBodiesPredicate = options.analyzeFunctionBodiesPredicate;
     cacheSize = options.cacheSize;
     dart2jsHint = options.dart2jsHint;
     enableAssertMessage = options.enableAssertMessage;
     enableAsync = options.enableAsync;
     enableStrictCallChecks = options.enableStrictCallChecks;
     enableGenericMethods = options.enableGenericMethods;
     enableSuperMixins = options.enableSuperMixins;
     enableTiming = options.enableTiming;
-    enableTrailingCommas = options.enableTrailingCommas;
     generateImplicitErrors = options.generateImplicitErrors;
     generateSdkErrors = options.generateSdkErrors;
     hint = options.hint;
     incremental = options.incremental;
     incrementalApi = options.incrementalApi;
     incrementalValidation = options.incrementalValidation;
     lint = options.lint;
     preserveComments = options.preserveComments;
     strongMode = options.strongMode;
     if (options is AnalysisOptionsImpl) {
@@ skipping 1352 matching lines @@
    * The data that was created from the source.
    */
   final E data;
 
   /**
    * Initialize a newly created holder to associate the given [data] with the
    * given [modificationTime].
    */
   TimestampedData(this.modificationTime, this.data);
 }