Simplify constructors translation, improve code style.

editor/util/plugins/com.google.dart.java2dart/resources/java_io.dart

 library java.io;
 
 import "dart:io";
 
 class JavaSystemIO {
   static Map<String, String> _properties = new Map();
   static String getProperty(String name) {
     {
       String value = _properties[name];
       if (value != null) {
@@ skipping 87 matching lines @@
     if (_newDirectory().existsSync()) {
       return true;
     }
     return false;
   }
   bool isDirectory() {
     return _newDirectory().existsSync();
   }
   Uri toURI() => new Uri(path: _path.toString());
   String readAsStringSync() => _newFile().readAsStringSync();
-  int lastModified() => _newFile().lastModifiedSync().millisecondsSinceEpoch;
+  int lastModified() {
+    if (!_newFile().existsSync()) return 0;
+    return _newFile().lastModifiedSync().millisecondsSinceEpoch;
+
+  }
   List<JavaFile> listFiles() {
     List<JavaFile> files = [];
     List<FileSystemEntity> entities = _newDirectory().listSync();
     for (FileSystemEntity entity in entities) {
       files.add(new JavaFile(entity.path));
     }
     return files;
   }
   File _newFile() => new File.fromPath(_path);
   Directory _newDirectory() => new Directory.fromPath(_path);
 }