topic lists: Add get_stream_name() to topic list widget.

frontend_tests/node_tests/topic_list.js

@@ -35,6 +35,7 @@ global.compile_template('topic_list_item');
     var topic_html = widget.get_dom();
 
     assert.equal(widget.get_parent(), parent_elem);
+    assert.equal(widget.get_stream_name(), 'devel');
 
     var topic = $(topic_html).find('a').text().trim();
     assert.equal(topic, 'coding');

static/js/topic_list.js

@@ -94,6 +94,10 @@ exports.build_widget = function (parent_elem, stream, active_topic, max_topics)
         return stream === stream_name;
     };
 
+    self.get_stream_name = function () {
+        return stream;
+    };
+
     self.get_dom = function () {
         return self.dom;
     };