Make standalone tests not dependent on current working directory.

tests/standalone/io/file_input_stream_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.
 // Testing file input stream, VM-only, standalone test.
 
 import "dart:convert";
 import "dart:io";
 
 import "package:async_helper/async_helper.dart";
 import "package:expect/expect.dart";
 
 // Helper method to be able to run the test from the runtime
 // directory, or the top directory.
-String getFilename(String path) =>
-    new File(path).existsSync() ? path : '../$path';
+String getFilename(String path) {
+  var testPath = Platform.script.resolve('../../../$path');
+  return new File.fromUri(testPath).existsSync()
+      ? testPath.toFilePath()
+      : Platform.script.resolve('../../../runtime/$path').toFilePath();
+}
 
 void testStringLineSplitter() {
   String fileName = getFilename("tests/standalone/io/readuntil_test.dat");
   // File contains "Hello Dart\nwassup!\n"
   File file = new File(fileName);
   int linesRead = 0;
   var lineStream = file.openRead()
     .transform(UTF8.decoder)
     .transform(new LineSplitter());
   lineStream.listen((line) {
@@ skipping 233 matching lines @@
   testInputStreamDelete();
   testInputStreamAppend();
   testInputStreamOffset();
   testInputStreamBadOffset();
   // Check the length of these files as both are text files where one
   // is without a terminating line separator which can easily be added
   // back if accidentally opened in a text editor.
   testStringLineSplitterEnding("readline_test1.dat", 111);
   testStringLineSplitterEnding("readline_test2.dat", 114);
 }