The update is copied from an update we made to a Google-internal
client: cl/260202900

The update will save 1 shader compilation.

This should help solve our regression:
https://github.com/flutter/flutter/issues/31203

More regressions on iOS might be introduced later by
https://github.com/flutter/engine/pull/9813#issuecomment-520039890

Unfortunately, we didn't rebase our benchmarks so such regressions
were not detected.

Hence to fully solve https://github.com/flutter/flutter/issues/31203,
we might need to revert some change in
https://github.com/flutter/engine/pull/9813 to make iOS shader warm-up
happen on the GPU thread again.