Avoid analysis server crash when reanalyze invoked during analysis.

pkg/analysis_server/test/analysis_server_test.dart

Index: pkg/analysis_server/test/analysis_server_test.dart
diff --git a/pkg/analysis_server/test/analysis_server_test.dart b/pkg/analysis_server/test/analysis_server_test.dart
index b138eb661693fe13b1ab81b4a2fd329e8b0ee178..44c52deee9043a88ebedb54a35de45a54e5d9a5c 100644
--- a/pkg/analysis_server/test/analysis_server_test.dart
+++ b/pkg/analysis_server/test/analysis_server_test.dart
@@ -94,6 +94,7 @@ main() {
       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');