This reverts commit d056500b.

This reverts commit 31de052e.

This reverts commit e2490f29.

Remove references to `Window`, and switch usages to `PlatformDispatcher` or `SingletonFlutterWindow` (#69617)

* Remove references to dart:ui.Window, and point usages to PlatformDispatcher or SingletonFlutterWindow, as appropriate

* remove new test platform dispatchers

* Amend documentation

* extract engine sub-metrics; change reported metrics

- Extract sub-metrics reported by the Web engine: "preroll_frame", "apply_frame".
- Add a concept of unreported metrics: displayed on the benchmark UI, but not on the dashboard.
- Make "sceneBuildDuration" and "windowRenderDuration" unreported, which are too fine-grained. They are included in "drawFrameDuration" already.
- Report outlier ratio instead of outlier average. The ratio is more useful of the two.

* web benchmarks: separate outliers to reduce noise; add visualization

Collect chrome://tracing data in Web benchmarks

Initial web benchmark harness and 3 benchmarks