Roll external/skia 81e7bf8d6..8c19238a0 (2 commits)

https://skia.googlesource.com/skia.git/+log/81e7bf8d6..8c19238a0

2017-10-06 reed@google.com experiments to speed up drawing 32bit images into 565
2017-10-03 scroggo@google.com Bring android/o-mr1-release up to date for HEIF

Test: Presubmit checks in addition to passing all Skia test suites
Bug: 64884885
Merged-In: I4a4ab16de50d1ceb1ad87126590d6ef5a884e718
Change-Id: Id7d5a9e889771a9db3112e847439e395ae4aa614