Optionally log message send times on the client

(imported from commit 900a513496b7796173a7685a55b110b63024f574)

static/js/compose.js

@@ -355,7 +355,11 @@ function send_message() {
         request.to = JSON.stringify([request.to]);
     }
 
+    var start_time = new Date();
     function success() {
+        if (feature_flags.log_send_times) {
+            blueslip.log("send time: " + (new Date() - start_time));
+        }
         $("#new_message_content").val('').focus();
         autosize_textarea();
         $("#send-status").hide(0);

static/js/feature_flags.js

@@ -17,6 +17,9 @@ var customer4_realms = [
 ];
 var is_customer4 = _.contains(customer4_realms, page_params.domain);
 
+// Manually-flipped debugging flags
+exports.log_send_times = false;
+
 // Permanent realm-specific stuff:
 
 exports.twenty_four_hour_time = internal_24_hour_people || iceland;