Bug 1271084 - Apply ESLint autofixes to ignored /devtools files. r=tromey

For simple rules like function spacing, we can auto-fix these across the code
base so they are followed in a consistent way.

To generate this patch, I ran:

./mach eslint devtools --no-ignore --fix

After this, I reverted any changes to third party files that we really do want
to ignore.

MozReview-Commit-ID: 6Q8BApkAW20

devtools/shared/async-utils.js

@@ -29,7 +29,7 @@ var Promise = require("promise");
  */
 exports.asyncOnce = function asyncOnce(func) {
   const promises = new WeakMap();
-  return function(...args) {
+  return function (...args) {
     let promise = promises.get(this);
     if (!promise) {
       promise = Task.spawn(func.apply(this, args));
@@ -53,11 +53,11 @@ exports.asyncOnce = function asyncOnce(func) {
  *         happens
  */
 exports.listenOnce = function listenOnce(element, event, useCapture) {
-  return new Promise(function(resolve, reject) {
-    var onEvent = function(ev) {
+  return new Promise(function (resolve, reject) {
+    var onEvent = function (ev) {
       element.removeEventListener(event, onEvent, useCapture);
       resolve(ev);
-    }
+    };
     element.addEventListener(event, onEvent, useCapture);
   });
 };