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

tests/standalone/io/print_sync_test.dart

Index: tests/standalone/io/print_sync_test.dart
diff --git a/tests/standalone/io/print_sync_test.dart b/tests/standalone/io/print_sync_test.dart
index f709df606fab78cd9e389c85f924a00d5f28a2e1..05f8014d7ba9a013dfe86f79c6ec9841a1cbb882 100644
--- a/tests/standalone/io/print_sync_test.dart
+++ b/tests/standalone/io/print_sync_test.dart
@@ -10,7 +10,8 @@ import "package:async_helper/async_helper.dart";
 void main() {
   asyncStart();
   Process.run(Platform.executable,
-              [Platform.script.resolve('print_sync_script.dart').toFilePath()])
+              [new Uri.file(Platform.script)
+                   .resolve('print_sync_script.dart').toString()])
       .then((out) {
         asyncEnd();
         Expect.equals(1002, out.stdout.split('\n').length);