Implement the new '??' operator in analyzer.

pkg/analyzer/lib/src/generated/incremental_resolver.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 engine.incremental_resolver;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/src/generated/constant.dart';
@@ skipping 1147 matching lines @@
       timer.stop('verify');
     }
   }
 }
 
 class PoorMansIncrementalResolver {
   final TypeProvider _typeProvider;
   final Source _unitSource;
   final DartEntry _entry;
   final CompilationUnit _oldUnit;
+  final AnalysisOptions _options;
   CompilationUnitElement _unitElement;
 
   int _updateOffset;
   int _updateDelta;
   int _updateEndOld;
   int _updateEndNew;
 
   List<AnalysisError> _newScanErrors = <AnalysisError>[];
   List<AnalysisError> _newParseErrors = <AnalysisError>[];
 
   PoorMansIncrementalResolver(this._typeProvider, this._unitSource, this._entry,
-      this._oldUnit, bool resolveApiChanges) {
+      this._oldUnit, bool resolveApiChanges, this._options) {
     _resolveApiChanges = resolveApiChanges;
   }
 
   /**
    * Attempts to update [_oldUnit] to the state corresponding to [newCode].
    * Returns `true` if success, or `false` otherwise.
    * The [_oldUnit] might be damaged.
    */
   bool resolve(String newCode) {
     logger.enter('diff/resolve $_unitSource');
@@ skipping 192 matching lines @@
     // resolve references in the comment
     incrementalResolver._resolveReferences(newComment);
     // OK
     return true;
   }
 
   Token _scan(String code) {
     RecordingErrorListener errorListener = new RecordingErrorListener();
     CharSequenceReader reader = new CharSequenceReader(code);
     Scanner scanner = new Scanner(_unitSource, reader, errorListener);
+    scanner.enableNullAwareOperators = _options.enableNullAwareOperators;
     Token token = scanner.tokenize();
     _newScanErrors = errorListener.errors;
     return token;
   }
 
   /**
    * Set the given [comment] as a "precedingComments" for [token].
    */
   void _setPrecedingComments(Token token, CommentToken comment) {
     if (token is BeginTokenWithComment) {
@@ skipping 436 matching lines @@
   @override
   String toString() => name;
 }
 
 class _TokenPair {
   final _TokenDifferenceKind kind;
   final Token oldToken;
   final Token newToken;
   _TokenPair(this.kind, this.oldToken, this.newToken);
 }