return the promise returned by then to guarantee order

src/browser/telemetry.js

@@ -388,7 +388,7 @@ Instrumenter.prototype.instrumentNetwork = function() {
 
         // Start our handler before returning the promise. This allows resp.clone()
         // to execute before other handlers touch the response.
-        promise.then(function (resp) {
+        promise = promise.then(function (resp) {
           metadata.end_time_ms = _.now();
           metadata.status_code = resp.status;
           metadata.response_content_type = resp.headers.get('Content-Type');