Revert "Remove generalized gradient code"

This reverts commit 0c63006b88a16e3418d92852a62771615799839d.

BUG=skia:
NOTREECHECKS=true
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2235953003

Review-Url: https://codereview.chromium.org/2235953003
2 files changed