<!--IssueSummary start--> <details> <summary> Everyone can contribute. [Help move this issue forward](https://handbook.gitlab.com/handbook/marketing/developer-relations/contributor-success/community-contributors-workflows/#contributor-links) while earning points, leveling up and collecting rewards. </summary> - [Close this issue](https://contributors.gitlab.com/manage-issue?action=close&projectId=278964&issueIid=402772) </details> <!--IssueSummary end--> <!-- This template is a great use for issues that are feature::additions or technical tasks for larger issues.--> ### Context While discussing LCP metrics in our ~"Performance Round Table::Source Code" call, we noticed some unexpected differences explained by not having the same element trigger the LCP metric due to varying lengths of content. We noticed we still haven't added any marks/measures from User Timings API like we've done in other apps. These would allow us to discern better the changes in specific performance of our app. ### Example | Where? | Screenshot | | ------ | ------ | | Browser console |  | | Sitespeed report (metrics) |  | ### Proposal * Add marks/measures to the file tree listing screen * Add marks/measures to the blob view screen ### Marks and measures | Type | Screen | Name of metric | | ------ | ------ | ------ | | Mark | File tree | Show first file | | Mark | File tree | Show last file | | Mark | File tree | Show commit | | Measure | File tree | Rendering full list | | Mark | Blob | Start blob content rendering | | Mark | Blob | Finish blob content rendering | | Mark | Blob | Show commit | | Mark | Blob | Show codeowners | | Measure | Blob | Rendering full blob content | (proposals, please feel free to tweak and edit and add/remove as necessary) <!-- Use this section to explain the feature and how it will work. It can be helpful to add technical details, design proposals, and links to related epics or issues. --> <!-- Consider adding related issues and epics to this issue. You can also reference the Feature Proposal Template (https://gitlab.com/gitlab-org/gitlab/-/blob/master/.gitlab/issue_templates/Feature%20proposal%20-%20detailed.md) for additional details to consider adding to this issue. Additionally, as a data oriented organization, when your feature exits planning breakdown, consider adding the `What does success look like, and how can we measure that?` section. --> <!-- Label reminders Use the following resources to find the appropriate labels: - Use only one tier label choosing the lowest tier this is intended for - https://gitlab.com/gitlab-org/gitlab/-/labels - https://about.gitlab.com/handbook/product/categories/features/ -->