Use std::unique_ptr.

TBR=reed@google.com

Committed: https://skia.googlesource.com/skia/+/20c1e3abfc681771f73eb19fde7284196e028940

Committed: https://skia.googlesource.com/skia/+/3dd9ed37c24611af86f0fe374bd3698b63f09450
GOLD_TRYBOT_URL= https://gold.skia.org/search2?unt=true&query=source_type%3Dgm&master=false&issue=1780933003

Review URL: https://codereview.chromium.org/1780933003
18 files changed