Use correct types on cloned constructors in mixin applications.

pkg/front_end/test/fasta/bootstrap_test.dart

 // Copyright (c) 2017, the Dart project authors.  Please see the AUTHORS file
 // for details. All rights reserved. Use of this source code is governed by a
 // BSD-style license that can be found in the LICENSE file.
 
 import 'dart:async' show Future;
 
 import 'dart:io' show Directory, File, Platform;
 
 import 'dart:isolate' show Isolate;
 
 import 'package:async_helper/async_helper.dart' show asyncEnd, asyncStart;
 
 import 'package:front_end/src/fasta/testing/kernel_chain.dart'
     show computePatchedSdk;
 
 import 'package:testing/testing.dart' show StdioProcess;
 
 import 'package:kernel/binary/ast_from_binary.dart' show BinaryBuilder;
 
 import 'package:kernel/ast.dart' show Program;
 
 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");
   Uri compiledOnceOutput = tmp.uri.resolve("fasta1.dill");
   Uri compiledTwiceOutput = tmp.uri.resolve("fasta2.dill");
   Uri outlineOutput = tmp.uri.resolve("outline.dill");
   try {
     await runCompiler(sourceCompiler, sourceCompiler, compiledOnceOutput);
     await runCompiler(compiledOnceOutput, sourceCompiler, compiledTwiceOutput);
     await compare(compiledOnceOutput, compiledTwiceOutput);
@@ skipping 16 matching lines @@
   Uri patchedSdk = await computePatchedSdk();
   Uri dartVm = Uri.base.resolve(Platform.resolvedExecutable);
   StdioProcess result = await StdioProcess.run(dartVm.toFilePath(), <String>[
     "-c",
     compiler.toFilePath(),
     "--compile-sdk=${patchedSdk.toFilePath()}",
     "--output=${output.toFilePath()}",
     "--verify",
     input.toFilePath(),
   ]);
-  print(result.output);
+  if (result.output.isNotEmpty) {
+    print(result.output);
+  }
   if (result.exitCode != 0) {
     throw "Compilation failed.";
   }
 }
 
 Future compare(Uri a, Uri b, {bool silent: false}) async {
   List<int> bytesA = await new File.fromUri(a).readAsBytes();
   List<int> bytesB = await new File.fromUri(b).readAsBytes();
   if (bytesA.length == bytesB.length) {
     bool same = true;
@@ skipping 29 matching lines @@
 }
 
 class ComparisonFailed {
   final Uri a;
   final Uri b;
 
   ComparisonFailed(this.a, this.b);
 
   toString() => "Error: $a is different from $b";
 }