Use JavaFile instead of Dart File.

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

 library java.engine.io;
 
 import "dart:io";
+import "java_io.dart";
 
 
 class OSUtilities {
   static bool isWindows() => Platform.operatingSystem == 'windows';
   static bool isMac() => Platform.operatingSystem == 'macos';
 }
 
 class FileUtilities2 {
-  static File createFile(String path) => new File(path);
+  static JavaFile createFile(String path) => new JavaFile(path);
 }