Extract code to summary.js.

(imported from commit 51d958b27e53555f5f77d6e6b661eade57190e23)

static/js/summary.js

@@ -0,0 +1,27 @@
+var summary = (function () {
+
+// This module has helper functions for the August 2013 message
+// summarizing experiment.
+
+var exports = {};
+
+exports.maybe_mark_summarized = function (message) {
+    if (feature_flags.summarize_read_while_narrowed) {
+        if (narrow.narrowed_by_reply()) {
+            // Narrowed to a topic or PM recipient
+            send_summarize_in_stream(message);
+        }
+
+        if (narrow.active() && !narrow.narrowed_to_search()) {
+            // Narrowed to anything except a search
+            send_summarize_in_home(message);
+        }
+    }
+};
+
+
+return exports;
+}());
+if (typeof module !== 'undefined') {
+    module.exports = summary;
+}