Add 'owner' field to sockets, that point to a potential IO resource using that Socket.

runtime/bin/vmservice/client/lib/src/elements/io_view.dart

Index: runtime/bin/vmservice/client/lib/src/elements/io_view.dart
diff --git a/runtime/bin/vmservice/client/lib/src/elements/io_view.dart b/runtime/bin/vmservice/client/lib/src/elements/io_view.dart
index 431fa25c924022014328b3f69b7de6da1f4643e6..492cc70add85da2bafb7689898515a172649f9ee 100644
--- a/runtime/bin/vmservice/client/lib/src/elements/io_view.dart
+++ b/runtime/bin/vmservice/client/lib/src/elements/io_view.dart
@@ -21,6 +21,11 @@ class IOViewElement extends ObservatoryElement {
   }
 }
 
+@CustomTag('io-ref')
+class IORefElement extends ServiceRefElement {
+  IORefElement.created() : super.created();
+}
+
 @CustomTag('io-http-server-list-view')
 class IOHttpServerListViewElement extends ObservatoryElement {
   @published ServiceMap list;