Test that safe saves are picked up by pub serve.

sdk/lib/_internal/pub_generated/test/serve/native_watch_replaced_file_test.dart

Index: sdk/lib/_internal/pub_generated/test/serve/native_watch_replaced_file_test.dart
diff --git a/sdk/lib/_internal/pub_generated/test/serve/native_watch_replaced_file_test.dart b/sdk/lib/_internal/pub_generated/test/serve/native_watch_replaced_file_test.dart
new file mode 100644
index 0000000000000000000000000000000000000000..b25721690f0fce764f6cf15bf87bc116470fdd34
--- /dev/null
+++ b/sdk/lib/_internal/pub_generated/test/serve/native_watch_replaced_file_test.dart
@@ -0,0 +1,57 @@
+// Copyright (c) 2013, the Dart project authors.  Please see the AUTHORS d.file
+// for details. All rights reserved. Use of this source code is governed by a
+// BSD-style license that can be found in the LICENSE file.
+
+library pub_tests;
+
+import 'dart:async';
+import 'dart:io';
+
+import 'package:path/path.dart' as p;
+import 'package:scheduled_test/scheduled_test.dart';
+
+import '../descriptor.dart' as d;
+import '../test_pub.dart';
+import 'utils.dart';
+
+main() {
+  // This is a regression test for http://dartbug.com/21402.
+  initConfig();
+  withBarbackVersions("any", () {
+    integration(
+        "picks up files replaced after serving started when using the "
+            "native watcher",
+        () {
+      d.dir(appPath, [d.pubspec({
+          "name": "myapp",
+          "transformers": ["myapp/src/transformer"]
+        }),
+            d.dir("lib", [d.dir("src", [d.file("transformer.dart", REWRITE_TRANSFORMER)])]),
+            d.dir("web", [d.file("file.txt", "before"),]),
+            d.file("other", "after")]).create();
+
+      createLockFile("myapp", pkg: ["barback"]);
+
+      pubServe(args: ["--no-force-poll"]);
+      waitForBuildSuccess();
+      requestShouldSucceed("file.out", "before.out");
+
+      schedule(() {
+        // Replace file.txt by renaming other on top of it.
+        return new File(
+            p.join(
+                sandboxDir,
+                appPath,
+                "other")).rename(p.join(sandboxDir, appPath, "web", "file.txt"));
+      });
+
+      // Read the transformed file to ensure the change is actually noticed by
+      // pub and not that we just get the new file contents piped through
+      // without pub realizing they've changed.
+      waitForBuildSuccess();
+      requestShouldSucceed("file.out", "after.out");
+
+      endPubServe();
+    });
+  });
+}