Bootstrap to extend WTF:RefPtr's run-time adoption checking to skia's SkRefCnt

With this change, refIfNotNull will now call RequireAdoption on the referenced
object in order to enable run-time adoption checking.  This is essential for
skia's SkRefCnt, which cannot have adoption checks enabled by default because
skia does not always use smart pointers internally, and has no explicit
notion of reference adoption.

BUG=304265

Review URL: https://codereview.chromium.org/25589003

git-svn-id: svn://svn.chromium.org/blink/trunk@159028 bbb929c8-8fbe-4397-9dbb-9b2b20218538