Switch analysis_server to use 'package:test'.

pkg/analysis_server/benchmark/perf/completion_timing_tests.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 server.performance.analysis.timing;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:args/args.dart';
-import 'package:unittest/unittest.dart';
+import 'package:test/test.dart';
 
 import '../../test/utils.dart';
 import 'performance_tests.dart';
 
 /**
  * Pass in the directory of the source to be analyzed as option `--source`,
  * specify a priority file with `--priority` and an offset for completions
  * with a `--offset`.
  */
 main(List<String> arguments) {
@@ skipping 53 matching lines @@
     sendAnalysisSetPriorityFiles([priorityFile]);
     sendCompletionGetSuggestions(priorityFile, offset);
 
     await analysisFinished;
 
     print('analysis completed in ${stopwatch.elapsed}');
     print('completion received at : $timings');
     await shutdown();
   }
 }