Roll external/skia 4f29c20f2..968af43f7 (6 commits)
https://skia.googlesource.com/skia.git/+log/4f29c20f2..968af43f7
2017-07-18 mtklein@chromium.org remove gather_i8, unify memory-touching contexts
2017-07-18 reed@google.com fix android-only function
2017-07-18 bsalomon@google.com Revert "Revert "Revert "Improvements to GPU dither."""
2017-07-18 brianosman@google.com Revert "Revert "remove dead code for legacy image encode api""
2017-07-18 bsalomon@google.com Revert "Revert "Improvements to GPU dither.""
2017-07-18 rmistry@google.com Copy over private SKPs during SKP asset create command
Test: Presubmit checks will test this change.
Change-Id: I774f4221486da2c55a96b755f44baa3367e07cf7