Add support for watch events and error notifications

pkg/analysis_server/lib/src/plugin/notification_manager.dart

Index: pkg/analysis_server/lib/src/plugin/notification_manager.dart
diff --git a/pkg/analysis_server/lib/src/plugin/notification_manager.dart b/pkg/analysis_server/lib/src/plugin/notification_manager.dart
index 53d0513091eedaac9de602b99826646ca4772743..99271317efa95de8b92654f3784e909cdff4521f 100644
--- a/pkg/analysis_server/lib/src/plugin/notification_manager.dart
+++ b/pkg/analysis_server/lib/src/plugin/notification_manager.dart
@@ -173,6 +173,17 @@ class NotificationManager {
                     converter.convertOutline(outline))
                 .toList());
         break;
+      case plugin.PLUGIN_NOTIFICATION_ERROR:
+        plugin.PluginErrorParams params =
+            new plugin.PluginErrorParams.fromNotification(notification);
+        // TODO(brianwilkerson) There is no indication for the client as to the
+        // fact that the error came from a plugin, let alone which plugin it
+        // came from. We should consider whether we really want to send them to
+        // the client.
+        channel.sendNotification(new server.ServerErrorParams(
+                params.isFatal, params.message, params.stackTrace)
+            .toNotification());
+        break;
     }
   }