The new A4-9210C and A6-9220C are based on the old Stoney-Ridge series from 2016. Compared to the old non-C variants, the new APUs feature lower performance and clock rate to achieve a reduced TDP of 6 Watt. That, however could enable passively cooled devices.
https://www.notebookcheck.net/AMD-announces-two-new-Chromebook-CPUs.391766.0.html
Already can find benchmarks at.Geekbench database under "Google grunt" codename or simply use the processor model number. Didn't AMD earlier dissed Chromebooks because of margins? It looks like they found a good way of clearing out old unwanted Bulldozer derived processors.