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

pkg/analyzer/lib/src/plugin/engine_plugin.dart

Index: pkg/analyzer/lib/src/plugin/engine_plugin.dart
diff --git a/pkg/analyzer/lib/src/plugin/engine_plugin.dart b/pkg/analyzer/lib/src/plugin/engine_plugin.dart
index 545064a86bb94eb131b6e6606e8cd3d0f978a6bf..145c4aae127202503780dc889dd10244af2fe460 100644
--- a/pkg/analyzer/lib/src/plugin/engine_plugin.dart
+++ b/pkg/analyzer/lib/src/plugin/engine_plugin.dart
@@ -224,6 +224,7 @@ class EnginePlugin implements Plugin {
     registerExtension(taskId, ReadyLibraryElement6Task.DESCRIPTOR);
     registerExtension(taskId, ReadyResolvedUnitTask.DESCRIPTOR);
     registerExtension(taskId, ResolveConstantExpressionTask.DESCRIPTOR);
+    registerExtension(taskId, ResolveDirectiveElementsTask.DESCRIPTOR);
     registerExtension(taskId, ResolveInstanceFieldsInUnitTask.DESCRIPTOR);
     registerExtension(taskId, ResolveLibraryReferencesTask.DESCRIPTOR);
     registerExtension(taskId, ResolveLibraryTask.DESCRIPTOR);