Add test directive to include other files used by a test in its compiled output directory.

tests/standalone/io/resolve_symbolic_links_test.dart

Index: tests/standalone/io/resolve_symbolic_links_test.dart
diff --git a/tests/standalone/io/resolve_symbolic_links_test.dart b/tests/standalone/io/resolve_symbolic_links_test.dart
index 690cbc522908062abb8a6bc7d7a9a4ab8e7f2f6c..4d3f22e8674b258ebe460e0e7a3be52c024657ed 100644
--- a/tests/standalone/io/resolve_symbolic_links_test.dart
+++ b/tests/standalone/io/resolve_symbolic_links_test.dart
@@ -11,7 +11,8 @@ import 'dart:async';
 import 'dart:io';
 
 main() {
-  String testsDir = Platform.script.resolve('../..').toFilePath();
+  String testsDir = Directory.current.uri.resolve('tests').toFilePath();
+
   // All of these tests test that resolveSymbolicLinks gives a path
   // that points to the same place as the original, and that it removes
   // all links, .., and . segments, and that it produces an absolute path.