Add plugin support for occurrences (and fix typo)

pkg/analyzer_plugin/test/plugin/test_all.dart

Index: pkg/analyzer_plugin/test/plugin/test_all.dart
diff --git a/pkg/analyzer_plugin/test/plugin/test_all.dart b/pkg/analyzer_plugin/test/plugin/test_all.dart
index f0b12832ad3061b76d1f6da24a2d6c17b0e3f640..e28d35eec9973d66a17147a28f980f37cb64e4f4 100644
--- a/pkg/analyzer_plugin/test/plugin/test_all.dart
+++ b/pkg/analyzer_plugin/test/plugin/test_all.dart
@@ -10,6 +10,7 @@ import 'fix_mixin_test.dart' as fix_mixin_test;
 import 'highlights_mixin_test.dart' as highlights_mixin_test;
 import 'kythe_mixin_test.dart' as kythe_mixin_test;
 import 'navigation_mixin_test.dart' as navigation_mixin_test;
+import 'occurrences_mixin_test.dart' as occurrences_mixin_test;
 import 'outline_mixin_test.dart' as outline_mixin_test;
 import 'plugin_test.dart' as plugin_test;
 
@@ -21,6 +22,7 @@ main() {
     highlights_mixin_test.main();
     kythe_mixin_test.main();
     navigation_mixin_test.main();
+    occurrences_mixin_test.main();
     outline_mixin_test.main();
     plugin_test.main();
   }, name: 'plugin');