Roll external/skia a4f3e14d8..1478f74aa (3 commits)

https://skia.googlesource.com/skia.git/+log/a4f3e14d8..1478f74aa

2017-05-03 mtklein@chromium.org Revert "treat SkPMColor as sRGB in SkPM4f::FromPMColor()"
2017-05-03 bsalomon@google.com Revert "Revert "Add a new non-AA rect op that does not inherit from GrLegacyMeshDrawOp.""
2017-05-03 recipe-roller@chromium.org Roll recipe dependencies (trivial).

Test: Presubmit checks will test this change.
Change-Id: I5e8714470ff7cc8ae1b28d387ddf6666ec8257af