Add an analysis server option to enable null-aware-operator support.

pkg/analysis_server/lib/src/domain_analysis.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 domain.analysis;
 
 import 'dart:async';
 
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/computer/computer_hover.dart';
@@ skipping 188 matching lines @@
   }
 
   /**
    * Implement the 'analysis.updateOptions' request.
    */
   Response updateOptions(Request request) {
     // options
     var params = new AnalysisUpdateOptionsParams.fromRequest(request);
     AnalysisOptions newOptions = params.options;
     List<OptionUpdater> updaters = new List<OptionUpdater>();
+    if (newOptions.enableNullAwareOperators != null) {
+      updaters.add((engine.AnalysisOptionsImpl options) {
+        options.enableNullAwareOperators = newOptions.enableNullAwareOperators;
+      });
+    }
     if (newOptions.generateDart2jsHints != null) {
       updaters.add((engine.AnalysisOptionsImpl options) {
         options.dart2jsHint = newOptions.generateDart2jsHints;
       });
     }
     if (newOptions.generateHints != null) {
       updaters.add((engine.AnalysisOptionsImpl options) {
         options.hint = newOptions.generateHints;
       });
     }
     server.updateOptions(updaters);
     return new AnalysisUpdateOptionsResult().toResponse(request.id);
   }
 }