Make standalone tests not dependent on current working directory.

tests/standalone/io/file_invalid_arguments_test.dart

Index: tests/standalone/io/file_invalid_arguments_test.dart
diff --git a/tests/standalone/io/file_invalid_arguments_test.dart b/tests/standalone/io/file_invalid_arguments_test.dart
index 58c6d7c423e54fa9f8a66fb082b823244cf69161..335e5748754f43d6a6b37f5286d6c942b5207a1d 100644
--- a/tests/standalone/io/file_invalid_arguments_test.dart
+++ b/tests/standalone/io/file_invalid_arguments_test.dart
@@ -99,7 +99,10 @@ void testFileSystemEntity() {
 }
 
 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() {