refactor: Add compare_function to buddy_list.

We were passing this in before, but having it as
a data member reinforces the idea that we'll want
this to be a first-class concept in the list, since
we depend on ordering for various things.

frontend_tests/node_tests/buddy_list.js

@@ -1,4 +1,5 @@
 set_global('$', global.make_zjquery());
+zrequire('buddy_data');
 zrequire('buddy_list');
 
 run_test('get_items', () => {

static/js/activity.js

@@ -218,7 +218,6 @@ exports.insert_user_into_list = function (user_id) {
     buddy_list.insert_or_move({
         key: user_id,
         item: info,
-        compare_function: buddy_data.compare_function,
     });
 
     exports.update_scrollbar.users();

static/js/buddy_list.js

@@ -34,6 +34,8 @@ var buddy_list = (function () {
         return data;
     };
 
+    self.compare_function = buddy_data.compare_function;
+
     // Try to keep code below this line generic, so that we can
     // extract a widget.
 
@@ -100,13 +102,12 @@ var buddy_list = (function () {
 
     self.find_position = function (opts) {
         var key = opts.key;
-        var compare_function = opts.compare_function;
         var i;
 
         for (i = 0; i < self.keys.length; i += 1) {
             var list_key = self.keys[i];
 
-            if (compare_function(key, list_key) < 0) {
+            if (self.compare_function(key, list_key) < 0) {
                 return i;
             }
         }
@@ -130,13 +131,11 @@ var buddy_list = (function () {
     self.insert_or_move = function (opts) {
         var key = opts.key.toString();
         var item = opts.item;
-        var compare_function = opts.compare_function;
 
         self.maybe_remove_key({key: key});
 
         var pos = self.find_position({
             key: key,
-            compare_function: compare_function,
         });
 
         // Order is important here--get the other_key