[Impeller] Occasional frame times ~2 orders of magnitude slower. #136849
Description
When running my Android TV app through Impeller, I generally see raster thread times of ~2ms. Every now and then, though (once about every 600 frames), I see a SUPER slow frame (~170ms). For example, see frame 6966 in this trace, where it looks like FenceWaiterVK::AddFence took 171ms 793µs
Observed at flutter/engine@e57b5ba
System info at https://gist.github.com/tvolkert/fc62a64356da50204843fe7231a925b5