Add strong mode type checking pass.

test/baseline_tester.dart

 // Copyright (c) 2016, 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:io';
 
 import 'package:kernel/analyzer/loader.dart';
 import 'package:kernel/kernel.dart';
 import 'package:kernel/target/targets.dart';
 import 'package:kernel/text/ast_to_text.dart';
 import 'package:path/path.dart' as pathlib;
 import 'package:test/test.dart';
 import 'package:kernel/checks.dart';
 
 final String inputDirectory = 'testcases/input';
 
 /// A target to be used for testing.
 ///
 /// To simplify testing dependencies, we avoid transformations that rely on
 /// a patched SDK or any SDK changes that have not landed in the main SDK.
 abstract class TestTarget extends Target {
   /// Annotations to apply on the textual output.
   Annotator get annotator => null;
+
+  List<String> transformProgram(Program program);
 }
 
 void runBaselineTests(String folderName, TestTarget target) {
   String outputDirectory = 'testcases/$folderName';
   String sdk = pathlib.dirname(pathlib.dirname(Platform.resolvedExecutable));
   var batch = new DartLoaderBatch();
   Directory directory = new Directory(inputDirectory);
   for (FileSystemEntity file in directory.listSync()) {
     if (file is File && file.path.endsWith('.dart')) {
       String name = pathlib.basename(file.path);
       test(name, () async {
         String dartPath = file.path;
         String shortName = pathlib.withoutExtension(name);
         String filenameOfBaseline = '$outputDirectory/$shortName.baseline.txt';
         String filenameOfCurrent = '$outputDirectory/$shortName.current.txt';
 
         var repository = new Repository();
         var loader = await batch.getLoader(
             repository,
             new DartOptions(
                 strongMode: target.strongMode,
                 sdk: sdk,
                 declaredVariables: target.extraDeclaredVariables));
         var program = loader.loadProgram(dartPath, target: target);
         runSanityChecks(program);
-        target.transformProgram(program);
+        var errors = target.transformProgram(program);
         runSanityChecks(program);
 
         var buffer = new StringBuffer();
+        for (var error in errors) {
+          buffer.writeln('// $error');
+        }
         new Printer(buffer, annotator: target.annotator)
             .writeLibraryFile(program.mainMethod.enclosingLibrary);
         String current = '$buffer';
         new File(filenameOfCurrent).writeAsStringSync(current);
 
         var baselineFile = new File(filenameOfBaseline);
         if (!baselineFile.existsSync()) {
           new File(filenameOfBaseline).writeAsStringSync(current);
         } else {
           var baseline = baselineFile.readAsStringSync();
           if (baseline != current) {
             fail('Output of `$name` changed for $folderName.\n'
                 'Command to reset the baseline:\n'
                 '  rm $filenameOfBaseline\n'
                 'Command to see the diff:\n'
                 '  diff -cd $outputDirectory/$shortName.{baseline,current}.txt'
                 '\n');
           }
         }
       });
     }
   }
 }