SkBitSet: make movable.

Change-Id: Iaf05d652b5bb8d99db3d51d1d9009e1de27ed7a3
Reviewed-on: https://skia-review.googlesource.com/123025
Reviewed-by: Ben Wagner <bungeman@google.com>
Commit-Queue: Ben Wagner <bungeman@google.com>
Auto-Submit: Hal Canary <halcanary@google.com>
2 files changed