fix: Remove synchronous operation with file system. (#879)

This patch:
- introduces `helper.promisify` - a simple polyfill for the `util.promisify`. The 
  `util.promisify` could not be used due to Node6 compatibility issues.
- migrates all sync filesystem operations to the async replicas

Fixes #884.

lib/Launcher.js

@@ -15,7 +15,7 @@
  */
 const os = require('os');
 const path = require('path');
-const removeSync = require('rimraf').sync;
+const removeFolder = require('rimraf');
 const childProcess = require('child_process');
 const Downloader = require('../utils/ChromiumDownloader');
 const {Connection} = require('./Connection');
@@ -26,6 +26,9 @@ const {helper} = require('./helper');
 // @ts-ignore
 const ChromiumRevision = require('../package.json').puppeteer.chromium_revision;
 
+const mkdtempAsync = helper.promisify(fs.mkdtemp);
+const removeFolderAsync = helper.promisify(removeFolder);
+
 const CHROME_PROFILE_PATH = path.join(os.tmpdir(), 'puppeteer_dev_profile-');
 
 const DEFAULT_ARGS = [
@@ -69,7 +72,7 @@ class Launcher {
 
     if (!options.args || !options.args.some(arg => arg.startsWith('--user-data-dir'))) {
       if (!options.userDataDir)
-        temporaryUserDataDir = fs.mkdtempSync(CHROME_PROFILE_PATH);
+        temporaryUserDataDir = await mkdtempAsync(CHROME_PROFILE_PATH);
 
       chromeArguments.push(`--user-data-dir=${options.userDataDir || temporaryUserDataDir}`);
     }
@@ -107,12 +110,16 @@ class Launcher {
       chromeProcess.stderr.pipe(process.stderr);
     }
 
-    const waitForChromeToClose = new Promise(fulfill => {
+    const waitForChromeToClose = new Promise((fulfill, reject) => {
       chromeProcess.once('close', () => {
         // Cleanup as processes exit.
-        if (temporaryUserDataDir)
-          removeSync(temporaryUserDataDir);
-        fulfill();
+        if (temporaryUserDataDir) {
+          removeFolderAsync(temporaryUserDataDir)
+              .then(() => fulfill())
+              .catch(err => console.error(err));
+        } else {
+          fulfill();
+        }
       });
     });
 
@@ -153,7 +160,7 @@ class Launcher {
       if (temporaryUserDataDir) {
         // Attempt to remove temporary profile directory to avoid littering.
         try {
-          removeSync(temporaryUserDataDir);
+          removeFolder.sync(temporaryUserDataDir);
         } catch (e) { }
       }
       return waitForChromeToClose;