Right now PictureLayers are only cached if they meet the cache criteria for 2+ frames. In the case of particularly complex pictures, like SVGs, this can lead to 2+ frames of rendering jank.

We should allow an opt in, either by re-using the underspecified is_complex flag, or by introducing another, to always cache on the first frame.

c.f. https://github.com/flutter/engine/blob/master/flow/raster_cache.cc#L272