Fixes leak of native File objects.

tests/standalone/io/file_lock_test.dart

Index: tests/standalone/io/file_lock_test.dart
diff --git a/tests/standalone/io/file_lock_test.dart b/tests/standalone/io/file_lock_test.dart
index d84ca2b3f10123f9592a155f2c740b1625417be3..ca590c1fd512a1eb20ebef23fc46d2760d6de4bc 100644
--- a/tests/standalone/io/file_lock_test.dart
+++ b/tests/standalone/io/file_lock_test.dart
@@ -36,11 +36,11 @@ check(String path, int start, int end, FileLock mode, {bool locked}) {
 }
 
 checkLocked(String path,
-            [int start, int end, FileLock mode = FileLock.EXCLUSIVE]) =>
+    [int start = 0, int end = -1, FileLock mode = FileLock.EXCLUSIVE]) =>
     check(path, start, end, mode, locked: true);
 
 checkNotLocked(String path,
-               [int start, int end, FileLock mode = FileLock.EXCLUSIVE]) =>
+    [int start = 0, int end = -1, FileLock mode = FileLock.EXCLUSIVE]) =>
     check(path, start, end, mode, locked: false);
 
 void testLockWholeFile() {