simplify library element accessor

pkg/analysis_server/lib/src/services/completion/dart/completion_manager.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 services.completion.dart.manager;
 
 import 'dart:async';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
 import 'package:analysis_server/src/provisional/completion/completion_core.dart'
@@ skipping 97 matching lines @@
   @override
   Expression dotTarget;
 
   @override
   Source librarySource;
 
   @override
   CompletionTarget target;
 
   @override
-  Future<LibraryElement> get libraryElement async {
+  LibraryElement get libraryElement {
     //TODO(danrubel) build the library element rather than all the declarations
     CompilationUnit unit = target.unit;
     if (unit != null) {
       CompilationUnitElement elem = unit.element;
       if (elem != null) {
         return elem.library;
       }
     }
     return null;
   }
@@ skipping 78 matching lines @@
         dotTarget = node.realTarget;
       }
     }
     if (node is PrefixedIdentifier) {
       if (identical(node.identifier, target.entity)) {
         dotTarget = node.prefix;
       }
     }
   }
 }