Selectively run ESLint on js/background.js

Enabling ESLint on a per function basis allows us to incrementally improve the codebase
without requiring large and potentially risky refactorings.

.eslintignore

@@ -15,5 +15,6 @@ test/views/*.js
 /*.js
 
 # ES2015+ files
+!js/background.js
 !main.js
 !prepare_build.js

js/background.js

@@ -1,3 +1,17 @@
+/* eslint-disable */
+
+/* eslint-env browser */
+
+/* global Backbone: false */
+/* global $: false */
+
+/* global ConversationController: false */
+/* global getAccountManager: false */
+/* global storage: false */
+/* global textsecure: false */
+/* global Whisper: false */
+/* global wrapDeferred: false */
+
 /*
  * vim: ts=4:sw=4:expandtab
  */
@@ -482,9 +496,12 @@
         });
     }
 
+  /* eslint-enable */
+  /* jshint ignore:start */
   async function onMessageReceived(ev) {
     const { data } = ev;
 
+    // eslint-disable-next-line no-bitwise
     if (data.message.flags & textsecure.protobuf.DataMessage.Flags.PROFILE_KEY_UPDATE) {
       const profileKey = data.message.profileKey.toArrayBuffer();
       const sender = ConversationController.getOrCreateAndWait(data.source, 'private');
@@ -495,6 +512,7 @@
 
     const message = initIncomingMessage(data);
     const isDuplicate = await isMessageDuplicate(message);
+
     if (isDuplicate) {
       console.log('Received duplicate message', message.idForLogging());
       // TODO: Is `ev.confirm` a `Promise`? Original code didn’t return it:
@@ -524,6 +542,8 @@
       { initialLoadComplete }
     );
   }
+  /* jshint ignore:end */
+  /* eslint-disable */
 
     function onSentMessage(ev) {
         var now = new Date().getTime();