Revert "Change dart:io Platform.script to return a Uri."

tests/standalone/io/windows_environment_test.dart

Index: tests/standalone/io/windows_environment_test.dart
diff --git a/tests/standalone/io/windows_environment_test.dart b/tests/standalone/io/windows_environment_test.dart
index f3a5c058732bcdc50a0a3efe9de017fc7f438c77..7df329464623f23ed0ab16bcc0bd75b39d8df266 100644
--- a/tests/standalone/io/windows_environment_test.dart
+++ b/tests/standalone/io/windows_environment_test.dart
@@ -18,9 +18,8 @@ set SCRIPTDIR=%~dp0
 %1 %2
       """);
   var dart = Platform.executable;
-  var script = Platform.script
-                       .resolve('windows_environment_script.dart')
-                       .toFilePath();
+  var script = join(dirname(Platform.script),
+                    'windows_environment_script.dart');
   Process.run('cmd',
               ['/c', funkyFile.path, dart, script]).then((p) {
     if (0 != p.exitCode) throw "Exit code not 0";