Avoid spurious "The compiler crashed" messages in batch mode.

tests/compiler/dart2js/dart2js_batch_test.dart

 // Copyright (c) 2014, 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';
 import 'dart:convert';
 import 'dart:io';
 
 import 'package:path/path.dart' as path;
 import 'package:async_helper/async_helper.dart';
@@ skipping 56 matching lines @@
   process.stdin.writeln('--out="$outFile" "$inFile"');
   process.stdin.writeln('--out="$outFile2" "$inFile"');
   process.stdin.writeln('too many arguments');
   process.stdin.writeln(r'"non existing file.dart"');
   process.stdin.close();
   Future<String> output = process.stdout.transform(UTF8.decoder).join();
   Future<String> errorOut = process.stderr.transform(UTF8.decoder).join();
   return Future.wait([output, errorOut])
         .then((result) {
       String stdoutOutput = result[0];
-      print('out:\n$stdoutOutput');
       String stderrOutput = result[1];
-      print('err:\n$stderrOutput');
 
       Expect.equals(4, ">>> EOF STDERR".allMatches(stderrOutput).length);
       Expect.equals(4, ">>>".allMatches(stderrOutput).length);
 
       Expect.equals(2, ">>> TEST OK".allMatches(stdoutOutput).length);
       Expect.equals(2, ">>> TEST FAIL".allMatches(stdoutOutput).length);
       Expect.equals(4, ">>>".allMatches(stdoutOutput).length);
     });
 }
 
 void main() {
   var tmpDir;
   asyncTest(() {
     return setup()
         .then(launchDart2Js)
         .then(runTests)
         .whenComplete(cleanUp);
   });
 }