[ VM / DartDev ] Default to port 8181 for DDS

Change-Id: I5356e962895add05663752e3f062181ded669dd0
Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/147922
Reviewed-by: Ryan Macnak <rmacnak@google.com>

pkg/dartdev/lib/src/commands/run.dart

@@ -254,7 +254,7 @@ class _DebuggingSession {
   Uri _bindAddress = Uri.http('127.0.0.1', '');
   DartDevelopmentService _dds;
   bool _observe = false;
-  int _port = 0;
+  int _port = 8181;
   Process _process;
   Uri _serviceInfoUri;
   Future _stderrDone;