fix typo

tests/standalone/io/test_extension_test.dart

Index: tests/standalone/io/test_extension_test.dart
diff --git a/tests/standalone/io/test_extension_test.dart b/tests/standalone/io/test_extension_test.dart
index 552a6b334c8e6e600fc0a96f4cb6bb089ccbd631..276cbc9f0c40b44afb38022c3d9dbd6a4cb0a50c 100644
--- a/tests/standalone/io/test_extension_test.dart
+++ b/tests/standalone/io/test_extension_test.dart
@@ -54,7 +54,7 @@ void main() {
   }).chain((_) {
     Path script = testDirectory.append('test_extension_tester.dart');
     return Process.run(options.executable, [script.toNativePath()]);
-  })..then((processResult result) {
+  })..then((ProcessResult result) {
     Expect.equals(0, result.exitCode);
     tempDirectory.deleteSync(recursive: true);
   })..handleException((_) {