Fix 'Location' sort order for annotations

1398661 extracted the code for getting a location from an annotation
into a separate module. However that function expects an Annotation but
the sort predicate function was being passed a Thread.

Consequently the predicate function was returning
Number.POSITIVE_INFINITY for every thread and so sort ordering fell back
to the default 'tie-breaker' comparator - which is the original index of
the element in the list being sorted.

Fixes #3106

h/static/scripts/app-controller.js

@@ -89,7 +89,9 @@ module.exports = function AppController(
         predicateFn = ['-!!message', 'message.updated'];
         break;
       case 'Location':
-        predicateFn = annotationMetadata.location;
+        predicateFn = function (thread) {
+          return annotationMetadata.location(thread.message);
+        };
         break;
     }
     $scope.sort = {

h/static/scripts/polyfills.js

@@ -3,6 +3,7 @@
 // ES2015 polyfills
 require('core-js/es6/promise');
 require('core-js/fn/array/find');
+require('core-js/fn/array/find-index');
 require('core-js/fn/object/assign');
 
 // URL constructor, required by IE 10/11,

h/static/scripts/test/app-controller-test.js

 'use strict';
 
 var angular = require('angular');
+var proxyquire = require('proxyquire');
 
+var annotationFixtures = require('./annotation-fixtures');
 var events = require('../events');
+var util = require('./util');
 
 describe('AppController', function () {
   var $controller = null;
   var $scope = null;
   var $rootScope = null;
+  var fakeAnnotationMetadata = null;
   var fakeAnnotationUI = null;
   var fakeAuth = null;
   var fakeDrafts = null;
@@ -28,9 +32,18 @@ describe('AppController', function () {
     return $controller('AppController', locals);
   };
 
-  before(function () {
-    return angular.module('h', [])
-      .controller('AppController', require('../app-controller'))
+  beforeEach(function () {
+    fakeAnnotationMetadata = {
+      location: function () { return 0; },
+    };
+
+    var AppController = proxyquire('../app-controller', util.noCallThru({
+      'angular': angular,
+      './annotation-metadata': fakeAnnotationMetadata,
+    }));
+
+    angular.module('h', [])
+      .controller('AppController', AppController)
       .controller('AnnotationUIController', angular.noop);
   });
 
@@ -263,4 +276,24 @@ describe('AppController', function () {
       assert.equal(fakeWindow.confirm.callCount, 0);
     });
   });
+
+  describe('sorting', function () {
+    function annotationThread() {
+      return {message: annotationFixtures.defaultAnnotation()};
+    }
+
+    it('sorts threads by location when sort name is "Location"', function () {
+      var threads = [annotationThread(), annotationThread()];
+      fakeAnnotationMetadata.location = function (annotation) {
+        return threads.findIndex(function (thread) {
+          return thread.message === annotation;
+        });
+      };
+      createController();
+      $scope.sort.name = 'Location';
+      $scope.$digest();
+      assert.equal($scope.sort.predicate(threads[0]), 0);
+      assert.equal($scope.sort.predicate(threads[1]), 1);
+    });
+  });
 });