Clean VM thread shutdown:

runtime/bin/vmservice/vmservice_io.dart

Index: runtime/bin/vmservice/vmservice_io.dart
diff --git a/runtime/bin/vmservice/vmservice_io.dart b/runtime/bin/vmservice/vmservice_io.dart
index 409bc5972a0c110d842c0da006e319a958bef8ff..d9b0c754f1735b403314209d7a5968e382249799 100644
--- a/runtime/bin/vmservice/vmservice_io.dart
+++ b/runtime/bin/vmservice/vmservice_io.dart
@@ -89,6 +89,15 @@ main() {
     // scheduled microtasks.
     Timer.run(() {});
   }
+  // TODO(johnmccutchan, turnidge) Creating a VMService object here causes
+  // strange behavior from the legacy debug protocol and coverage tool.
+  // Enable this code, and remove the call to Isolate::KillIsolate() from
+  // service_isolate.cc when the strange behavior is solved.
+  // See: https://github.com/dart-lang/sdk/issues/23977
+  // else {
+  //   var service = new VMService();
+  //   service.onShutdown = _onShutdown;
+  // }
   scriptLoadPort.handler = _processLoadRequest;
   // Register signal handler after a small delay to avoid stalling main
   // isolate startup.