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

headless/index.js

@@ -101,8 +101,8 @@ function startFlipper({
       // current eventloop task here.
       setTimeout(() => {
         exportStore(store)
-          .then(output => {
-            originalConsole.log(output);
+          .then(({serializedString}) => {
+            originalConsole.log(serializedString);
             process.exit();
           })
           .catch(console.error);
@@ -122,7 +122,9 @@ function startFlipper({
   if (exit == 'sigint') {
     process.on('SIGINT', async () => {
       try {
-        originalConsole.log(await exportStore(store));
+        const {serializedString, errorArray} = await exportStore(store);
+        errorArray.forEach(console.error);
+        originalConsole.log(serializedString);
       } catch (e) {
         console.error(e);
       }