Avoid analysis server crash when reanalyze invoked during analysis.

pkg/analysis_server/test/integration/integration_tests.dart

Index: pkg/analysis_server/test/integration/integration_tests.dart
diff --git a/pkg/analysis_server/test/integration/integration_tests.dart b/pkg/analysis_server/test/integration/integration_tests.dart
index a2e188ddf45e936d4c0b2c73d68bd755a35587af..4436253022f8643f65e5a555def93044f7bd84fd 100644
--- a/pkg/analysis_server/test/integration/integration_tests.dart
+++ b/pkg/analysis_server/test/integration/integration_tests.dart
@@ -154,6 +154,10 @@ abstract class AbstractAnalysisServerIntegrationTest extends
       expect(serverConnected.isCompleted, isFalse);
       serverConnected.complete();
     });
+    onServerError.listen((ServerErrorParams params) {
+      // A server error should never happen during an integration test.
+      fail(params.message);
+    });
     return server.start().then((_) {
       server.listenToOutput(dispatchNotification);
       server.exitCode.then((_) {