add back SkPacked16toX32 to SkColorPriv

Android vendor requires this interface
so moving it back to public for now.

TBR=reed@google.com
Bug: skia: 6898
Change-Id: I4eb6da0b929227fcf327dac0626e9efd8f9a2705
Reviewed-on: https://skia-review.googlesource.com/48420
Reviewed-by: Cary Clark <caryclark@skia.org>
Commit-Queue: Cary Clark <caryclark@skia.org>
2 files changed