[third] Don't move typeahead popups when the body scrolls.

Trac #1479

All our typeaheads use this, but I made it an option that must be enabled
explicitly since it is not default bootstrap behavior.

(imported from commit 97852dc407d1f6dbe46b5fdd2c56d3ed8c6718d2)

static/js/composebox_typeahead.js

@@ -214,6 +214,7 @@ exports.initialize = function () {
             return stream_data.subscribed_streams();
         },
         items: 3,
+        fixed: true,
         highlighter: function (item) {
             var query = this.query;
             return typeahead_helper.highlight_query_in_phrase(query, item);
@@ -232,6 +233,7 @@ exports.initialize = function () {
             return exports.topics_seen_for(stream_name);
         },
         items: 3,
+        fixed: true,
         highlighter: composebox_typeahead_highlighter,
         sorter: function (items) {
             var sorted = typeahead_helper.sorter(this.query, items, function (x){return x;});
@@ -246,6 +248,7 @@ exports.initialize = function () {
         source: page_params.people_list,
         items: 5,
         dropup: true,
+        fixed: true,
         highlighter: function (item) {
             var query = get_last_recipient_in_pm(this.query);
             var item_formatted = typeahead_helper.render_person(item);
@@ -339,6 +342,7 @@ exports.initialize = function () {
             }
         },
         dropup: true,
+        fixed: true,
         matcher: function (item) {
             if (this.completing === 'emoji') {
                 return query_matches_emoji(this.token, item);

static/js/search.js

@@ -52,6 +52,7 @@ exports.initialize = function () {
             search_object = suggestions.lookup_table;
             return suggestions.strings;
         },
+        fixed: true,
         items: 30,
         helpOnEmptyStrings: true,
         naturalSearch: true,

static/third/bootstrap/js/bootstrap.js

@@ -1826,6 +1826,11 @@
     this.source = this.options.source
     this.shown = false
     this.dropup = this.options.dropup
+    this.fixed = this.options.fixed || false;
+
+    if (this.fixed) {
+      this.$menu.css('position', 'fixed');
+    }
     // The naturalSearch option causes arrow keys to immediately
     // update the search box with the underlying values from the
     // search suggestions.
@@ -1854,7 +1859,16 @@
     }
 
   , show: function () {
-      var pos = $.extend({}, this.$element.offset(), {
+      var pos;
+
+      if (this.fixed) {
+        // Relative to screen instead of to page
+        pos = this.$element[0].getBoundingClientRect();
+      } else {
+        pos = this.$element.offset();
+      }
+
+      pos = $.extend({}, pos, {
         height: this.$element[0].offsetHeight
       })