Use correct types on cloned constructors in mixin applications.

pkg/front_end/test/fasta/bootstrap_test.dart

Index: pkg/front_end/test/fasta/bootstrap_test.dart
diff --git a/pkg/front_end/test/fasta/bootstrap_test.dart b/pkg/front_end/test/fasta/bootstrap_test.dart
index 265c6160ad4931dc9e58b7e876c84853118c886a..a5ba270fcd88a2096c93da29d7b1f1c6bae2b31c 100644
--- a/pkg/front_end/test/fasta/bootstrap_test.dart
+++ b/pkg/front_end/test/fasta/bootstrap_test.dart
@@ -23,7 +23,8 @@ import 'package:kernel/text/ast_to_text.dart' show programToString;
 
 Future main() async {
   asyncStart();
-  Uri sourceCompiler = Uri.base.resolve("pkg/front_end/tool/fasta/compile.dart");
+  Uri sourceCompiler =
+      Uri.base.resolve("pkg/front_end/tool/fasta/compile.dart");
   Uri outline = Uri.base.resolve("pkg/front_end/tool/fasta/outline.dart");
   Uri packages = await Isolate.packageConfig;
   Directory tmp = await Directory.systemTemp.createTemp("fasta_bootstrap");
@@ -60,7 +61,9 @@ Future runCompiler(Uri compiler, Uri input, Uri output) async {
     "--verify",
     input.toFilePath(),
   ]);
-  print(result.output);
+  if (result.output.isNotEmpty) {
+    print(result.output);
+  }
   if (result.exitCode != 0) {
     throw "Compilation failed.";
   }