Add a task to partially resolve a compilation unit

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

 // Copyright (c) 2015, 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.plugin.engine_plugin;
 
 import 'package:analyzer/plugin/task.dart';
 import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/src/task/general.dart';
 import 'package:analyzer/src/task/html.dart';
@@ skipping 64 matching lines @@
     registerExtension(taskId, ComputeConstantValueTask.DESCRIPTOR);
     registerExtension(taskId, ContainingLibrariesTask.DESCRIPTOR);
     registerExtension(taskId, DartErrorsTask.DESCRIPTOR);
     registerExtension(taskId, EvaluateUnitConstantsTask.DESCRIPTOR);
     registerExtension(taskId, GatherUsedImportedElementsTask.DESCRIPTOR);
     registerExtension(taskId, GatherUsedLocalElementsTask.DESCRIPTOR);
     registerExtension(taskId, GenerateHintsTask.DESCRIPTOR);
     registerExtension(taskId, LibraryErrorsReadyTask.DESCRIPTOR);
     registerExtension(taskId, LibraryUnitErrorsTask.DESCRIPTOR);
     registerExtension(taskId, ParseDartTask.DESCRIPTOR);
+    registerExtension(taskId, PartiallyResolveUnitReferencesTask.DESCRIPTOR);
     registerExtension(taskId, ResolveLibraryReferencesTask.DESCRIPTOR);
     registerExtension(taskId, ResolveLibraryTypeNamesTask.DESCRIPTOR);
     registerExtension(taskId, ResolveUnitReferencesTask.DESCRIPTOR);
     registerExtension(taskId, ResolveUnitTypeNamesTask.DESCRIPTOR);
     registerExtension(taskId, ResolveVariableReferencesTask.DESCRIPTOR);
     registerExtension(taskId, ScanDartTask.DESCRIPTOR);
     registerExtension(taskId, VerifyUnitTask.DESCRIPTOR);
     //
     // Register HTML tasks.
     //
     registerExtension(taskId, DartScriptsTask.DESCRIPTOR);
     registerExtension(taskId, HtmlErrorsTask.DESCRIPTOR);
     registerExtension(taskId, ParseHtmlTask.DESCRIPTOR);
   }
 
   /**
    * Validate the given extension by throwing an [ExtensionError] if it is not a
    * valid domain.
    */
   void _validateTaskExtension(Object extension) {
     if (extension is! TaskDescriptor) {
       String id = taskExtensionPoint.uniqueIdentifier;
       throw new ExtensionError('Extensions to $id must be a TaskDescriptor');
     }
   }
 }