Remove flag for enabling null-aware operators. They are now on by default.

pkg/compiler/lib/src/compiler.dart

 // Copyright (c) 2012, 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.
 
 part of dart2js;
 
 /**
  * If true, print a warning for each method that was resolved, but not
  * compiled.
  */
@@ skipping 773 matching lines @@
   final bool suppressWarnings;
   final bool fatalWarnings;
 
   /// If `true`, some values are cached for reuse in incremental compilation.
   /// Incremental compilation is basically calling [run] more than once.
   final bool hasIncrementalSupport;
 
   /// If `true` native extension syntax is supported by the frontend.
   final bool allowNativeExtensions;
 
-  /// Temporary flag to enable `?.`, `??`, and `??=` until it becomes part of
-  /// the spec.
-  final bool enableNullAwareOperators;
-
   /// Output provider from user of Compiler API.
   api.CompilerOutputProvider userOutputProvider;
 
   /// Generate output even when there are compile-time errors.
   final bool generateCodeWithCompileTimeErrors;
 
   /// The compiler is run from the build bot.
   final bool testMode;
 
   bool disableInlining = false;
@@ skipping 248 matching lines @@
             this.terseDiagnostics: false,
             this.deferredMapUri: null,
             this.dumpInfo: false,
             this.showPackageWarnings: false,
             this.useContentSecurityPolicy: false,
             this.suppressWarnings: false,
             this.fatalWarnings: false,
             bool hasIncrementalSupport: false,
             this.enableExperimentalMirrors: false,
             this.allowNativeExtensions: false,
-            this.enableNullAwareOperators: false,
             this.generateCodeWithCompileTimeErrors: false,
             this.testMode: false,
             api.CompilerOutputProvider outputProvider,
             List<String> strips: const []})
       : this.disableTypeInferenceFlag =
           disableTypeInferenceFlag || !emitJavaScript,
         this.analyzeOnly =
             analyzeOnly || analyzeSignaturesOnly || analyzeAllFlag,
         this.analyzeSignaturesOnly = analyzeSignaturesOnly,
         this.analyzeAllFlag = analyzeAllFlag,
@@ skipping 1445 matching lines @@
   InterfaceType streamType([DartType elementType]) {
     InterfaceType type = streamClass.computeType(compiler);
     if (elementType == null) {
       return streamClass.rawType;
     }
     return type.createInstantiation([elementType]);
   }
 }
 
 typedef void InternalErrorFunction(Spannable location, String message);