Make standalone tests not dependent on current working directory.

tests/standalone/io/file_invalid_arguments_test.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.
 
 import "dart:async";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
@@ skipping 81 matching lines @@
        FileSystemEntity.identical(x, y))([1,2,3], ".")))
   .then((_) => futureThrows(((x, y) =>
        FileSystemEntity.identical(x, y))(".", 52)))
   .then((_) => futureThrows(((x) => FileSystemEntity.isLink(x))(52)))
   .then((_) => futureThrows(((x) => FileSystemEntity.isFile(x))(52)))
   .then((_) => futureThrows(((x) => FileSystemEntity.isDirectory(x))(52)))
   .then((_) => asyncEnd());
 }
 
 String getFilename(String path) {
-  return new File(path).existsSync() ? path : 'runtime/$path';
+  var testPath = Platform.script.resolve('../../../$path');
+  return new File.fromUri(testPath).existsSync()
+      ? testPath.toFilePath()
+      : Platform.script.resolve('../../../runtime/$path').toFilePath();
 }
 
 main() {
   testReadInvalidArgs('asdf');
   testReadIntoInvalidArgs(12, 0, 1);
   testReadIntoInvalidArgs(new List(10), '0', 1);
   testReadIntoInvalidArgs(new List(10), 0, '1');
   testWriteByteInvalidArgs('asdf');
   testWriteFromInvalidArgs(12, 0, 1);
   testWriteFromInvalidArgs(new List(10), '0', 1);
   testWriteFromInvalidArgs(new List(10), 0, '1');
   testWriteStringInvalidArgs("Hello, world", 42);
   testFileSystemEntity();
 }