typeahead: Clear rendered stream html on stream rename.

Previously, after a stream name, you could search for it using its
new name but the typeahead would still display the old name.

frontend_tests/node_tests/typeahead_helper.js

@@ -520,6 +520,33 @@ run_test('render_stream', () => {
     assert(rendered);
 });
 
+run_test('clear_rendered_stream', () => {
+    var rendered = false;
+    var stream = {
+        description: 'This is a description.',
+        stream_id: 44,
+        name: 'Stream To Be Cleared',
+    };
+    global.stub_templates(function (template_name, args) {
+        assert.equal(template_name, 'typeahead_list_item');
+        assert.equal(args.primary, stream.name);
+        assert.equal(args.secondary, stream.description);
+        rendered = true;
+        return 'typeahead-item-stub';
+    });
+    assert.equal(th.render_stream(stream), 'typeahead-item-stub');
+    assert(rendered);
+
+    rendered = false;
+    assert.equal(th.render_stream(stream), 'typeahead-item-stub');
+    assert.equal(rendered, false);
+
+    // Here rendered will be true as it is being rendered again.
+    th.clear_rendered_stream(stream.stream_id);
+    assert.equal(th.render_stream(stream), 'typeahead-item-stub');
+    assert(rendered);
+});
+
 run_test('render_emoji', () => {
     // Test render_emoji with normal emoji.
     var rendered = false;

static/js/subs.js

@@ -149,6 +149,9 @@ exports.update_stream_name = function (sub, new_name) {
 
     // Update the message feed.
     message_live_update.update_stream_name(stream_id, new_name);
+
+    // Clear rendered typeahead cache
+    typeahead_helper.clear_rendered_stream(stream_id);
 };
 
 exports.update_stream_description = function (sub, description, rendered_description) {

static/js/typeahead_helper.js

@@ -132,6 +132,12 @@ exports.render_person_or_user_group = function (item) {
     return typeahead_helper.render_person(item);
 };
 
+exports.clear_rendered_stream = function (stream_id) {
+    if (rendered.streams.has(stream_id)) {
+        rendered.streams.del(stream_id);
+    }
+};
+
 exports.render_stream = function (stream) {
     var desc = stream.description;
     var short_desc = desc.substring(0, 35);