Use TaskInputBuilder to compute import/export source closures.

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/plugin.dart';
 import 'package:analyzer/plugin/task.dart';
 import 'package:analyzer/src/task/dart.dart';
 import 'package:analyzer/src/task/general.dart';
@@ skipping 49 matching lines @@
     // Register general tasks.
     //
     registerExtension(taskId, GetContentTask.DESCRIPTOR);
     //
     // Register Dart tasks.
     //
     registerExtension(taskId, BuildCompilationUnitElementTask.DESCRIPTOR);
     registerExtension(taskId, BuildDirectiveElementsTask.DESCRIPTOR);
     registerExtension(taskId, BuildEnumMemberElementsTask.DESCRIPTOR);
     registerExtension(taskId, BuildExportNamespaceTask.DESCRIPTOR);
-    registerExtension(taskId, BuildExportSourceClosureTask.DESCRIPTOR);
+    registerExtension(taskId, BuildSourceClosuresTask.DESCRIPTOR);
     registerExtension(taskId, BuildFunctionTypeAliasesTask.DESCRIPTOR);
     registerExtension(taskId, BuildLibraryElementTask.DESCRIPTOR);
     registerExtension(taskId, BuildPublicNamespaceTask.DESCRIPTOR);
     registerExtension(taskId, BuildTypeProviderTask.DESCRIPTOR);
     registerExtension(taskId, ParseDartTask.DESCRIPTOR);
     registerExtension(taskId, ResolveLibraryTypeNamesTask.DESCRIPTOR);
     registerExtension(taskId, ResolveUnitTypeNamesTask.DESCRIPTOR);
     registerExtension(taskId, ScanDartTask.DESCRIPTOR);
     //
     // Register HTML tasks.
     //
   }
 
   /**
    * 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');
     }
   }
 }