Timeout promise while exporting flipper plugin

Summary:
Added a promiseTimeout util so that we limit the time taken to export flipper plugin. I had received a feedback from the user stating that that the loader for the export stays for ages and never finishes. So this diff adds a timeout to the promise which is returned by `exportPersistedState` function. This function is currently implemented just by Layout inspector to fetch the entire view hierarchy. I suspect the the former mentioned bug may be due to the unresponsive client.

This diff also shows the plugin and the client information for which `exportPersistedState` timed out. Also this will hopefully solve the problem surfaced recently stating that the bug report gets stuck, the reason for which I suspect would be the same as the above mentioned reason, because we export flipper data when we create a bug report.

Reviewed By: danielbuechele

Differential Revision: D14712633

fbshipit-source-id: 35f8cfa722ec3b7ff94ebda943d618834ac3207d

src/utils/__tests__/promiseTimeout.node.js

@@ -0,0 +1,37 @@
+/**
+ * Copyright 2018-present Facebook.
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ * @format
+ */
+import promiseTimeout from '../promiseTimeout';
+
+test('test promiseTimeout for timeout to happen', () => {
+  let promise = promiseTimeout(
+    200,
+    new Promise((resolve, reject) => {
+      let id = setTimeout(() => {
+        clearTimeout(id);
+        resolve();
+      }, 500);
+      return 'Executed';
+    }),
+    'Timed out',
+  );
+  return expect(promise).rejects.toThrow('Timed out');
+});
+
+test('test promiseTimeout for timeout not to happen', () => {
+  let promise = promiseTimeout(
+    200,
+    new Promise((resolve, reject) => {
+      let id = setTimeout(() => {
+        clearTimeout(id);
+        resolve();
+      }, 100);
+      resolve('Executed');
+    }),
+    'Timed out',
+  );
+  return expect(promise).resolves.toBe('Executed');
+});