Get rid of the selected_message_class global

Instead we infer this from narrow.active(), with the ability to override during
the narrowing procedure.

(imported from commit fab9c6861f19aedf0ee8af094c1ef4e8a0a73d80)

tools/jslint/check-all.js

@@ -38,7 +38,7 @@ var globals =
     + ' update_autocomplete autocomplete_needs_update'
 
     // zephyr.js
-    + ' message_array message_dict selected_message_class'
+    + ' message_array message_dict'
     + ' clear_table add_to_table subject_dict'
     + ' keep_pointer_in_view move_pointer_at_page_top_and_bottom'
     + ' respond_to_message'

zephyr/static/js/narrow.js

@@ -32,6 +32,8 @@ exports.narrowing_type = function () {
 };
 
 function do_narrow(icon, description, filter_function) {
+    var was_narrowed = exports.active();
+
     narrowed = filter_function;
 
     // Your pointer isn't changed when narrowed.
@@ -58,8 +60,8 @@ function do_narrow(icon, description, filter_function) {
     // Indicate both which message is persistently selected and which
     // is temporarily selected
     select_message_by_id(selected_message_id,
-                         {then_scroll: false, update_server: false});
-    selected_message_class = "narrowed_selected_message";
+                         {then_scroll: false, update_server: false,
+                          for_narrow: was_narrowed});
     select_message_by_id(target_id,
                          {then_scroll: true, update_server: false});
 
@@ -154,7 +156,6 @@ exports.show_all_messages = function () {
     $("#searchbox").removeClass('narrowed_view');
     $("#show_all_messages").attr("disabled", "disabled");
     $("#currently_narrowed_to").html("");
-    selected_message_class = "selected_message";
     // Includes scrolling.
     select_message_by_id(persistent_message_id, {then_scroll: true});
 

zephyr/static/js/zephyr.js

@@ -3,7 +3,6 @@ var message_dict = {};
 var subject_dict = {};
 var people_hash = {};
 
-var selected_message_class = 'selected_message';
 var viewport = $(window);
 var reloading_app = false;
 
@@ -188,9 +187,14 @@ function send_pointer_update() {
 $(setTimeout(send_pointer_update, 1000));
 
 function update_selected_message(message, opts) {
-    opts = $.extend({}, {update_server: true}, opts);
-    $('.' + selected_message_class).removeClass(selected_message_class);
-    message.addClass(selected_message_class);
+    opts = $.extend({}, {
+        update_server: true,
+        for_narrow: narrow.active()
+    }, opts);
+
+    var cls = opts.for_narrow ? 'narrowed_selected_message' : 'selected_message';
+    $('.' + cls).removeClass(cls);
+    message.addClass(cls);
 
     var new_selected_id = rows.id(message);
     if (opts.update_server && !narrow.active()