Fix some analysis issues.

pkg/analysis_server/test/services/completion/dart/completion_contributor_util.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.
 
 import 'dart:async';
 
 import 'package:analysis_server/protocol/protocol_generated.dart';
 import 'package:analysis_server/src/ide_options.dart';
 import 'package:analysis_server/src/provisional/completion/dart/completion_dart.dart';
 import 'package:analysis_server/src/services/completion/completion_core.dart';
@@ skipping 562 matching lines @@
     }
     // We use a delayed future to allow microtask events to finish. The
     // Future.value or Future() constructors use scheduleMicrotask themselves and
     // would therefore not wait for microtask callbacks that are scheduled after
     // invoking this method.
     return new Future.delayed(
         Duration.ZERO, () => performAnalysis(times - 1, completer));
   }
 
   void resolveSource(String path, String content) {
-    Source libSource = addSource(path, content);
+    addSource(path, content);
   }
 
   @override
   void setUp() {
     super.setUp();
     contributor = createContributor();
   }
 }