add --x-package-warnings-prefix option to dartanalyzer

pkg/analyzer_cli/test/all.dart

Index: pkg/analyzer_cli/test/all.dart
diff --git a/pkg/analyzer_cli/test/all.dart b/pkg/analyzer_cli/test/all.dart
index 9f085630c8219386ca5b0a1d14cdc04558f89655..1fd1dd7d002db7458756ce716ca494165007615c 100644
--- a/pkg/analyzer_cli/test/all.dart
+++ b/pkg/analyzer_cli/test/all.dart
@@ -6,6 +6,7 @@ import 'boot_loader_test.dart' as boot_loader;
 import 'driver_test.dart' as driver;
 import 'error_test.dart' as error;
 import 'options_test.dart' as options;
+import 'package_prefix_test.dart' as package_prefix;
 import 'perf_report_test.dart' as perf;
 import 'plugin_manager_test.dart' as plugin_manager;
 import 'reporter_test.dart' as reporter;
@@ -26,4 +27,5 @@ main() {
   plugin_manager.main();
   reporter.main();
   super_mixin.main();
+  package_prefix.main();
 }