Rename SkCanvasDrawable to SkDrawable, and make public

 (patchset #2 id:20001 of https://codereview.chromium.org/903993002/)"

This reverts commit c4e87724920222a218f31b22612efc5b1ec0ed6c.

BUG=skia:
TBR=
NOTREECHECKS=True

Review URL: https://codereview.chromium.org/898343004
14 files changed