Added DebugLogger to testing scripts.

tools/testing/dart/utils.dart

 // Copyright (c) 2013, 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.
 
 library utils;
 
+import 'dart:io';
 import 'dart:utf' as utf;
 
+class DebugLogger {
+  static OutputStream _stream;
+
+  /**
+   * If [path] was null, the DebugLogger will write messages to stdout.
+   */
+  static init(Path path, {append: false}) {
+    if (path != null) {
+      var mode = append ? FileMode.APPEND : FileMode.WRITE;
+      _stream = new File.fromPath(path).openOutputStream(mode);
+    }
+  }
+
+  static void close() {
+    if (_stream != null) {
+      _stream.close();
+      _stream = null;
+    }
+  }
+
+  static void info(String msg) {
+    _print("Info: $msg");
+  }
+
+  static void warning(String msg) {
+    _print("Warning: $msg");
+  }
+
+  static void error(String msg) {
+    _print("Error: $msg");
+  }
+
+  static void _print(String msg) {
+    if (_stream != null) {
+      _stream.write(encodeUtf8(msg));
+      _stream.write([0x0a]);
+    } else {
+      print(msg);
+    }
+  }
+}
 
 List<int> encodeUtf8(String string) {
   return utf.encodeUtf8(string);
 }
 
 // TODO(kustermann,ricow): As soon we have a debug log we should log
 // invalid utf8-encoded input to the log.
 // Currently invalid bytes will be replaced by a replacement character.
 String decodeUtf8(List<int> bytes) {
   return utf.decodeUtf8(bytes);
 }