Track async causal stack traces

runtime/observatory/lib/src/repositories/target.dart

Index: runtime/observatory/lib/src/repositories/target.dart
diff --git a/runtime/observatory/lib/src/repositories/target.dart b/runtime/observatory/lib/src/repositories/target.dart
index 69290fcc6380a16894caaa39e91012090394a5f2..333e00dc09e38a32313ba560751ac6d5b2e927de 100644
--- a/runtime/observatory/lib/src/repositories/target.dart
+++ b/runtime/observatory/lib/src/repositories/target.dart
@@ -101,6 +101,10 @@ class TargetRepository implements M.TargetRepository {
   }
 
   static String _networkAddressOfDefaultTarget() {
+    if (!identical(1, 1.0)) {
+      // Dartium, assume we are developing.
+      return 'ws://127.0.0.1:8181/ws';
+    }
     Uri serverAddress = Uri.parse(window.location.toString());
     return 'ws://${serverAddress.authority}${serverAddress.path}ws';
   }