Dart: Uses tearDownAll in mojo_apptest.

mojo/dart/packages/mojo_apptest/lib/apptest.dart

Index: mojo/dart/packages/mojo_apptest/lib/apptest.dart
diff --git a/mojo/dart/packages/mojo_apptest/lib/apptest.dart b/mojo/dart/packages/mojo_apptest/lib/apptest.dart
index 7b4af0c9b5d73e344f7ad61d008966c475989277..9a260bdf1d1e7706d82d106012db9ab0b92adc38 100644
--- a/mojo/dart/packages/mojo_apptest/lib/apptest.dart
+++ b/mojo/dart/packages/mojo_apptest/lib/apptest.dart
@@ -36,10 +36,8 @@ class _ConnectionToShellApplication extends Application {
         testFunction(this, url);
       }
     });
-    // Append a final test to terminate shell connection.
-    // TODO(johnmccutchan): Remove this once package 'test' supports a global
-    // tearDown callback.
-    test('TERMINATE SHELL CONNECTION', () async {
+
+    tearDownAll(() async {
       await close();
       MojoHandle.reportLeakedHandles();
     });