Improve browser Total Blocking Time (TBT) performance of Project Merge Requests page into next tier

The Project Merge Requests page's browser Total Blocking Time (TBT) performance is unperformant:

* Environment:                10k
* Environment Version:        17.4.0-pre `7a6ca62cb98`
* Date:                       2024-08-21
NAME                                  | FCP (ms) | LCP (ms)       | TBT (ms)       | SI (ms) | LVC (ms) | TFR SIZE (kb) | SCORE | RESULT
--------------------------------------|----------|----------------|----------------|---------|----------|---------------|-------|-------
web_project_merge_requests            | 2063     | ✓ 2063 (<3600) | ✘ 533 (<500)   | 2158    | 3017     | 304.6         | 77    | FAILED

The Project Merge Requests page being tested can be seen here on Staging. Historically the page periodically fails threshold of 300ms for TBT:

Screenshot_2024-08-21_at_11.40.52

Older screenshot Screenshot_2024-07-02_at_13.05.10

Test Details

Testing was done on our 10k Reference Architecture environment with our lab condition SiteSpeed pipeline (named GitLab Browser Performance Tool internally). The project being tested is a copy of gitlabhq (tarball can be found here). GitLab Browser Performance Tool tests information is listed at Current test details page.

The latest GitLab Browser Performance pipeline results can always be found here. Through this page the full SiteSpeed report can be found via the SiteSpeed Report link on that page.

As per our performance targets this page's TBT metric is above the target of 300 ms which is severity4 . Task is to improve the page's browser performance into next tier.

Edited by 🤖 GitLab Bot 🤖