FBGlobalTransformCache: retry 3 times, wait between retries

Summary: That should improve the hit rate a little bit, notably for the cache-filling script. On OSS side, this changeset only adds the sleep() function as `FBGlobalTransformCache` is not exposed.

Reviewed By: cpojer

Differential Revision: D5201196

fbshipit-source-id: c2d8e1a1b03edd9e7747b3202c574b0783f4117d

packages/metro-bundler/src/lib/sleep.js

@@ -0,0 +1,20 @@
+/**
+ * Copyright (c) 2015-present, Facebook, Inc.
+ * All rights reserved.
+ *
+ * This source code is licensed under the BSD-style license found in the
+ * LICENSE file in the root directory of this source tree. An additional grant
+ * of patent rights can be found in the PATENTS file in the same directory.
+ *
+ * @flow
+ */
+
+'use strict';
+
+function sleep(duration: number): Promise<void> {
+  return new Promise(resolve => {
+    setTimeout(resolve, duration);
+  });
+}
+
+module.exports = sleep;