search pills: Narrow when typeahead is not used.

We can remove the typeahead by clicking outside the search box
after we have entered the search string to be filtered and then
focus on the searchbox  and press enter or just by pressing enter
on an empty string.

Previously, the narrow would just deactivate for the above condition
as the searchbox value which was passed as the raw_operators parameter
to the narrow.activate function was empty.
This happened because we called the activate function on pressing
enter for the keyup event, while the keydown event in the parent
container made a pill from the text and cleared the input. (as
mentioned in the comment for `KEY.ENTER` case in `input_pill.js`)

static/js/search.js

@@ -149,7 +149,17 @@ exports.initialize = function () {
             // operators.  (The reason the other actions don't call
             // this codepath is that they first all blur the box to
             // indicate that they've done what they need to do)
-            narrow.activate(Filter.parse(search_query_box.val()), {trigger: 'search'});
+
+            let operators = Filter.parse(search_query_box.val());
+            if (page_params.search_pills_enabled) {
+                // Pill is already added during keydown event of input pills.
+                // Thus we can't call narrow_or_search_for_term as the
+                // search_query_box has empty value.
+                const base_query = search_pill.get_search_string_for_current_filter(
+                    search_pill_widget.widget);
+                operators = Filter.parse(base_query);
+            }
+            narrow.activate(operators, {trigger: 'search'});
             search_query_box.blur();
             update_buttons_with_focus(false);
         }