Port most uses of SkOnce to SkLazyPtr. BUG=skia: Committed: http://code.google.com/p/skia/source/detail?r=15006 R=reed@google.com, mtklein@google.com Author: mtklein@chromium.org Review URL: https://codereview.chromium.org/304383005 git-svn-id: http://skia.googlecode.com/svn/trunk/include@15014 2bbb7eff-a529-9590-31e7-b0007b416f81