Revert[2] of "add backdrop option to SaveLayerRec"

Reverted because of picture/serialization failure

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1567063002

TBR=mtklein

Review URL: https://codereview.chromium.org/1567063002