Note: I'm not sure how this would work or how much work this entails. But it came up as a topic from conversations with @liyuqian, and we noticed there is no bug tracking it.

Use case

• Performance optimization: Running a Flutter app on the web and seeing some skipped frames, I'd like to reuse my knowledge of Flutter performance tools to start addressing the issue.
• Education: Writing docs about performance, I'd like to give the users two version of an app in DartPad. Users are able to bring up the performance overlay to see how one version of the app is performing much faster than the other one.

Proposal

• Enable the performance overlay for Flutter web apps.

For clarity, this is what I mean by performance overlay.

It is an engine layer added to a --profile (or --debug) version of an app by the engine. It shows the build times for the UI thread (a.k.a. main thread, app thread, etc.) and the GPU thread (a.k.a. raster thread -- i.e. not actually running on the GPU).