Don't run Analysis Server performance tests in checked mode.

pkg/analysis_server/benchmark/perf/performance_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;
 
 import 'dart:async';
 import 'dart:io';
 
 import 'package:analysis_server/plugin/protocol/protocol.dart';
@@ skipping 28 matching lines @@
     });
     onServerError.listen((ServerErrorParams params) {
       // A server error should never happen during an integration test.
       fail('${params.message}\n${params.stackTrace}');
     });
     Completer serverConnected = new Completer();
     onServerConnected.listen((_) {
       expect(serverConnected.isCompleted, isFalse);
       serverConnected.complete();
     });
-    return startServer().then((_) {
+    return startServer(checked: false).then((_) {
       server.listenToOutput(dispatchNotification);
       server.exitCode.then((_) {
         skipShutdown = true;
       });
       return serverConnected.future;
     });
   }
 
   /**
    * After every test, the server is stopped.
    */
   Future shutdown() async => await shutdownIfNeeded();
 
   /**
    * Enable [ServerService.STATUS] notifications so that [analysisFinished]
    * can be used.
    */
   Future subscribeToStatusNotifications() async {
     await sendServerSetSubscriptions([ServerService.STATUS]);
   }
 }
 
 class AbstractTimingTest extends AbstractAnalysisServerPerformanceTest {
   Future init(String source) async {
     await super.setUp();
     sourceDirectory = new Directory(source);
     return subscribeToStatusNotifications();
   }
 }