Beef up analysis server integration test messages.

pkg/analysis_server/test/timing/timing_framework.dart

Index: pkg/analysis_server/test/timing/timing_framework.dart
diff --git a/pkg/analysis_server/test/timing/timing_framework.dart b/pkg/analysis_server/test/timing/timing_framework.dart
index 757819d43c1e557bff1afc965f87ee1e69d2653b..cdf24fe351252ca7aaa5bf2d784a2a5e5a05666d 100644
--- a/pkg/analysis_server/test/timing/timing_framework.dart
+++ b/pkg/analysis_server/test/timing/timing_framework.dart
@@ -312,7 +312,7 @@ abstract class TimingTest extends IntegrationTestMixin {
     // doesn't exit, then forcibly terminate it.
     sendServerShutdown();
     return server.exitCode.timeout(SHUTDOWN_TIMEOUT, onTimeout: () {
-      return server.kill();
+      return server.kill('server failed to exit');
     });
   }
 }