Avoid analysis server crash when reanalyze invoked during analysis.

pkg/analysis_server/test/analysis_server_test.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.
 
 library test.analysis_server;
 
 import 'package:analyzer/file_system/physical_file_system.dart';
 import 'package:analysis_server/src/analysis_server.dart';
 import 'package:analysis_server/src/constants.dart';
 import 'package:analysis_server/src/domain_server.dart';
@@ skipping 76 matching lines @@
             expect(response.error, isNotNull);
           });
     });
 
     test('rethrow exceptions', () {
       AnalysisServerTestHelper helper = new AnalysisServerTestHelper();
       Exception exceptionToThrow = new Exception('test exception');
       MockServerOperation operation = new MockServerOperation(
           ServerOperationPriority.ANALYSIS, (_) { throw exceptionToThrow; });
       helper.server.operationQueue.add(operation);
+      helper.server.operationLoopRunning = true;
       try {
         helper.server.performOperation();
         fail('exception not rethrown');
       } on AnalysisException catch (exception) {
         expect(exception.cause.exception, equals(exceptionToThrow));
       }
     });
   });
 }
 
@@ skipping 11 matching lines @@
 
 class EchoHandler implements RequestHandler {
   @override
   Response handleRequest(Request request) {
     if (request.method == 'echo') {
       return new Response(request.id, result: {'echo': true});
     }
     return null;
   }
 }