Implement the new '??' operator in analyzer.

pkg/analyzer/lib/src/generated/incremental_resolver.dart

Index: pkg/analyzer/lib/src/generated/incremental_resolver.dart
diff --git a/pkg/analyzer/lib/src/generated/incremental_resolver.dart b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
index a4ff1f77084387695a7f8fadfbd3c43cd263ed04..02047c400c5983fec69b3ae0a2424d564560085c 100644
--- a/pkg/analyzer/lib/src/generated/incremental_resolver.dart
+++ b/pkg/analyzer/lib/src/generated/incremental_resolver.dart
@@ -1165,6 +1165,7 @@ class PoorMansIncrementalResolver {
   final Source _unitSource;
   final DartEntry _entry;
   final CompilationUnit _oldUnit;
+  final AnalysisOptions _options;
   CompilationUnitElement _unitElement;
 
   int _updateOffset;
@@ -1176,7 +1177,7 @@ class PoorMansIncrementalResolver {
   List<AnalysisError> _newParseErrors = <AnalysisError>[];
 
   PoorMansIncrementalResolver(this._typeProvider, this._unitSource, this._entry,
-      this._oldUnit, bool resolveApiChanges) {
+      this._oldUnit, bool resolveApiChanges, this._options) {
     _resolveApiChanges = resolveApiChanges;
   }
 
@@ -1389,6 +1390,7 @@ class PoorMansIncrementalResolver {
     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;