Port most uses of SkOnce to SkLazyPtr.

BUG=skia:

Committed: http://code.google.com/p/skia/source/detail?r=15006

Committed: http://code.google.com/p/skia/source/detail?r=15014

R=reed@google.com, mtklein@google.com

Author: mtklein@chromium.org

Review URL: https://codereview.chromium.org/304383005