Issue 26096. Explicitly compute the result that ensures that directives are resolved in units.

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 analyzer.src.generated.incremental_resolver;
 
 import 'dart:collection';
 import 'dart:math' as math;
 
 import 'package:analyzer/dart/ast/ast.dart';
@@ skipping 910 matching lines @@
         isByTask(LibraryErrorsReadyTask.DESCRIPTOR) ||
         isByTask(LibraryUnitErrorsTask.DESCRIPTOR) ||
         isByTask(ParseDartTask.DESCRIPTOR) ||
         isByTask(PartiallyResolveUnitReferencesTask.DESCRIPTOR) ||
         isByTask(PropagateVariableTypesInLibraryClosureTask.DESCRIPTOR) ||
         isByTask(PropagateVariableTypesInLibraryTask.DESCRIPTOR) ||
         isByTask(PropagateVariableTypesInUnitTask.DESCRIPTOR) ||
         isByTask(PropagateVariableTypeTask.DESCRIPTOR) ||
         isByTask(ScanDartTask.DESCRIPTOR) ||
         isByTask(ResolveConstantExpressionTask.DESCRIPTOR) ||
+        isByTask(ResolveDirectiveElementsTask.DESCRIPTOR) ||
         isByTask(ResolveInstanceFieldsInUnitTask.DESCRIPTOR) ||
         isByTask(ResolveLibraryReferencesTask.DESCRIPTOR) ||
         isByTask(ResolveLibraryTask.DESCRIPTOR) ||
         isByTask(ResolveLibraryTypeNamesTask.DESCRIPTOR) ||
         isByTask(ResolveUnitTask.DESCRIPTOR) ||
         isByTask(ResolveUnitTypeNamesTask.DESCRIPTOR) ||
         isByTask(ResolveVariableReferencesTask.DESCRIPTOR) ||
         isByTask(StrongModeVerifyUnitTask.DESCRIPTOR) ||
         isByTask(VerifyUnitTask.DESCRIPTOR)) {
       return DeltaResult.KEEP_CONTINUE;
@@ skipping 1277 matching lines @@
   @override
   String toString() => name;
 }
 
 class _TokenPair {
   final _TokenDifferenceKind kind;
   final Token oldToken;
   final Token newToken;
   _TokenPair(this.kind, this.oldToken, this.newToken);
 }