Add tools/ddbg_service.

runtime/bin/vmservice/observatory/lib/service_io.dart

Index: runtime/bin/vmservice/observatory/lib/service_io.dart
diff --git a/runtime/bin/vmservice/observatory/lib/service_io.dart b/runtime/bin/vmservice/observatory/lib/service_io.dart
index 77b7964f48e7e5a37e9bafe69c5d48ffa3f76ac8..5bae3e888f347ce587a55fb9fb5365dbd7b9e556 100644
--- a/runtime/bin/vmservice/observatory/lib/service_io.dart
+++ b/runtime/bin/vmservice/observatory/lib/service_io.dart
@@ -29,6 +29,8 @@ class _IOWebSocket implements CommonWebSocket {
           onDone: onClose,
           cancelOnError: true);
       onOpen();
+    }).catchError((e, st) {
+      onError();
     });
   }
   
@@ -40,7 +42,9 @@ class _IOWebSocket implements CommonWebSocket {
   }
   
   void close() {
-    _webSocket.close();
+    if (_webSocket != null) {
+      _webSocket.close();
+    }
   }
   
   Future<ByteData> nonStringToByteData(dynamic data) {