performance: Speed up search bar highlighting.

When we're highlighting all the people that show
up in a search from the search bar, we need
to fairly expensively build a regex from the
query:

    query = query.toLowerCase();
    query = query.replace(/[\-\[\]{}()*+?.,\\\^$|#\s]/g, '\\$&');
    const regex = new RegExp('(^' + query + ')', 'ig');

Even though the final regex is presumably cached, we
still needed to do that `query.replace` for every person.
Even for relatively small numbers of persons, this would
show up in profiles as expensive.

Now we just build the query once by using a pattern
where you call a function outside the loop to build
an inner function that's used in the loop that closes
on the `query` above.  The diff probably shows this
better than I explained it here.

static/js/search_suggestion.js

@@ -2,12 +2,15 @@ function stream_matches_query(stream_name, q) {
     return common.phrase_match(q, stream_name);
 }
 
-function highlight_person(query, person) {
+function make_person_highlighter(query) {
-    const hilite = typeahead_helper.highlight_query_in_phrase;
+    const hilite = typeahead_helper.make_query_highlighter(query);
+
+    return function (person) {
         if (settings_org.show_email()) {
-        return hilite(query, person.full_name) + " <" + hilite(query, person.email) + ">";
+            return hilite(person.full_name) + " <" + hilite(person.email) + ">";
         }
-    return hilite(query, person.full_name);
+        return hilite(person.full_name);
+    };
 }
 
 function match_criteria(operators, criteria) {
@@ -148,13 +151,15 @@ function get_group_suggestions(all_persons, last, operators) {
 
     const prefix = Filter.operator_to_prefix('pm-with', negated);
 
+    const highlight_person = make_person_highlighter(last_part);
+
     const suggestions = _.map(persons, function (person) {
         const term = {
             operator: 'pm-with',
             operand: all_but_last_part + ',' + person.email,
             negated: negated,
         };
-        const name = highlight_person(last_part, person);
+        const name = highlight_person(person);
         const description = prefix + ' ' + Handlebars.Utils.escapeExpression(all_but_last_part) + ',' + name;
         let terms = [term];
         if (negated) {
@@ -202,8 +207,10 @@ function get_person_suggestions(all_persons, last, operators, autocomplete_opera
 
     const prefix = Filter.operator_to_prefix(autocomplete_operator, last.negated);
 
+    const highlight_person = make_person_highlighter(query);
+
     const objs = _.map(persons, function (person) {
-        const name = highlight_person(query, person);
+        const name = highlight_person(person);
         const description = prefix + ' ' + name;
         const terms = [{
             operator: autocomplete_operator,

static/js/typeahead_helper.js

@@ -51,12 +51,13 @@ exports.highlight_with_escaping_and_regex = function (regex, item) {
     return result;
 };
 
-exports.highlight_query_in_phrase = function (query, phrase) {
+exports.make_query_highlighter = function (query) {
     let i;
     query = query.toLowerCase();
     query = query.replace(/[\-\[\]{}()*+?.,\\\^$|#\s]/g, '\\$&');
     const regex = new RegExp('(^' + query + ')', 'ig');
 
+    return function (phrase) {
         let result = "";
         const parts = phrase.split(' ');
         for (i = 0; i < parts.length; i += 1) {
@@ -67,6 +68,7 @@ exports.highlight_query_in_phrase = function (query, phrase) {
         }
         return result;
     };
+};
 
 exports.render_typeahead_item = function (args) {
     args.has_image = args.img_src !== undefined;