Reverts flutter/engine#50737

Initiated by: goderbauer

Reason for reverting: Fails in device lab, see https://logs.chromium.org/logs/flutter/buildbucket/cr-buildbucket/8755350727803344657/+/u/run_web_benchmarks_skwasm/stdout

Original PR Author: eyebrowsoffire

Reviewed By: {mdebbar, yjbanov}

This change reverts the following previous change:
Original Description:
Fixes https://github.com/flutter/flutter/issues/140429

Some notes here:
* Refactored the frame timing systems so that we can deal with asynchronous rendering.
* Consolidated rendering of multiple pictures in skwasm into a single call, so that the rasterization can be properly measured.
* Pulled the frame timings tests into the `ui` test suite so that they run on all renderers (including skwasm).