Make VM event streams look like real dart streams.

runtime/observatory/lib/service_common.dart

Index: runtime/observatory/lib/service_common.dart
diff --git a/runtime/observatory/lib/service_common.dart b/runtime/observatory/lib/service_common.dart
index 790efe1b3057982fe558db3f6f866003fcd24c56..0580f5cdbd08a21802eca79a8dcfcfa3b043a504 100644
--- a/runtime/observatory/lib/service_common.dart
+++ b/runtime/observatory/lib/service_common.dart
@@ -208,7 +208,8 @@ abstract class CommonWebSocketVM extends VM {
         return;
       }
       var event = map['event'];
-      postServiceEvent(event, data);
+      var streamId = map['streamId'];
+      postServiceEvent(streamId, event, data);
     });
   }
 
@@ -219,7 +220,8 @@ abstract class CommonWebSocketVM extends VM {
     }
     var event = map['event'];
     if (event != null) {
-      postServiceEvent(event, null);
+      var streamId = map['streamId'];
+      postServiceEvent(streamId, event, null);
       return;
     }