[files] Add retry with exponential backoff for file downloads in NM

Summary: See diff title

Test Plan: Run locally, verify that we backoff on failure

Reviewers: evan, spang, juan

Reviewed By: juan

Differential Revision: https://phab.nylas.com/D3887

src/K2

@@ -1 +1 @@
-Subproject commit 3390bc0783d7f17906a6884e4d757876a337506f
+Subproject commit 9f8aa0f42f031edc155a6e55d28edc6e008dc50c

src/flux/stores/file-download-store.es6

@@ -45,13 +45,18 @@ const THUMBNAIL_WIDTH = 320
 export class Download {
   static State = State
 
-  constructor({accountId, fileId, targetPath, filename, filesize, progressCallback}) {
+  constructor({accountId, fileId, targetPath, filename, filesize, progressCallback, retryWithBackoff}) {
     this.accountId = accountId;
     this.fileId = fileId;
     this.targetPath = targetPath;
     this.filename = filename;
     this.filesize = filesize;
     this.progressCallback = progressCallback;
+    this.retryWithBackoff = retryWithBackoff || false;
+    this.timeout = 15000;
+    this.maxTimeout = 2 * 60 * 1000;
+    this.attempts = 0;
+    this.maxAttempts = 10;
     if (!this.accountId) {
       throw new Error("Download.constructor: You must provide a non-empty accountId.");
     }
@@ -94,14 +99,22 @@ export class Download {
       const stream = fs.createWriteStream(this.targetPath);
       this.state = State.Downloading;
 
+      let startRequest = null;
+
       const onFailed = (err) => {
         this.request = null;
         stream.end();
+        if (!this.retryWithBackoff || this.attempts >= this.maxAttempts) {
           this.state = State.Failed;
           if (fs.existsSync(this.targetPath)) {
             fs.unlinkSync(this.targetPath);
           }
           reject(err);
+          return;
+        }
+
+        this.timeout = Math.min(this.maxTimeout, this.timeout * 2);
+        startRequest();
       };
 
       const onSuccess = () => {
@@ -112,6 +125,8 @@ export class Download {
         resolve(this);
       };
 
+      startRequest = () => {
+        console.info(`starting download with ${this.timeout}ms timeout`);
         const request = new NylasAPIRequest({
           api: NylasAPI,
           options: {
@@ -119,7 +134,9 @@ export class Download {
             path: `/files/${this.fileId}/download`,
             accountId: this.accountId,
             encoding: null, // Tell `request` not to parse the response data
+            timeout: this.timeout,
             started: (req) => {
+              this.attempts += 1;
               this.request = req;
               return progress(this.request, {throtte: 250})
               .on('progress', (prog) => {
@@ -150,6 +167,9 @@ export class Download {
         });
 
         request.run()
+      };
+
+      startRequest();
     });
     return this.promise
   }
@@ -233,6 +253,7 @@ class FileDownloadStore extends NylasStore {
       filename: file.displayName(),
       targetPath,
       progressCallback: () => this.trigger(),
+      retryWithBackoff: true,
     });
 
     // Do we actually need to queue and run the download? Queuing a download