Use SkUniqueCFRef in SkImage*CG.

This clarifies ownership and makes the code more readable.

It is safe to use unique_ptr directly for UniqueCFRef, since
unique_ptr does not call the deleter with nullptr.

Change-Id: I4326a86059fb31488d1e163faca95a6c29960039
Reviewed-on: https://skia-review.googlesource.com/155612
Commit-Queue: Hal Canary <halcanary@google.com>
Reviewed-by: Hal Canary <halcanary@google.com>
5 files changed