Update SkDescriptor

* add reset(const SkDescriptor&) to SkAutoDescriptor
* move impl to .cpp
* general updating of code

Change-Id: Id224d73456576927f78b4ba3afecc759c1fe3a1b
Reviewed-on: https://skia-review.googlesource.com/c/181175
Commit-Queue: Herb Derby <herb@google.com>
Reviewed-by: Robert Phillips <robertphillips@google.com>
3 files changed