Correct post deletion spec so it is async

app/assets/javascripts/discourse/models/post.js.es6

@@ -159,6 +159,7 @@ const Post = RestModel.extend({
     done elsewhere.
   **/
   setDeletedState(deletedBy) {
+    let promise;
     this.set('oldCooked', this.get('cooked'));
 
     // Moderators can delete posts. Users can only trigger a deleted at message, unless delete_removed_posts_after is 0.
@@ -169,8 +170,7 @@ const Post = RestModel.extend({
         can_delete: false
       });
     } else {
-
-      cookAsync(I18n.t("post.deleted_by_author", {count: Discourse.SiteSettings.delete_removed_posts_after})).then(cooked => {
+      promise = cookAsync(I18n.t("post.deleted_by_author", {count: Discourse.SiteSettings.delete_removed_posts_after})).then(cooked => {
         this.setProperties({
           cooked: cooked,
           can_delete: false,
@@ -181,6 +181,8 @@ const Post = RestModel.extend({
         });
       });
     }
+
+    return promise || Em.RSVP.Promise.resolve();
   },
 
   /**
@@ -203,11 +205,12 @@ const Post = RestModel.extend({
   },
 
   destroy(deletedBy) {
-    this.setDeletedState(deletedBy);
+    return this.setDeletedState(deletedBy).then(()=>{
       return ajax("/posts/" + this.get('id'), {
         data: { context: window.location.pathname },
         type: 'DELETE'
       });
+    });
   },
 
   /**

test/javascripts/models/post-test.js.es6

@@ -64,9 +64,9 @@ QUnit.test('destroy by non-staff', assert => {
       user = Discourse.User.create({username: 'evil trout'}),
       post = buildPost({user: user, cooked: originalCooked});
 
-  post.destroy(user);
-
+  return post.destroy(user).then(() => {
     assert.ok(!post.get('can_delete'), "the post can't be deleted again in this session");
     assert.ok(post.get('cooked') !== originalCooked, "the cooked content changed");
     assert.equal(post.get('version'), 2, "the version number increased");
+  });
 });