Roll external/skia 5af44defb..d81977f51 (4 commits)
https://skia.googlesource.com/skia.git/+log/5af44defb..d81977f51
2017-07-19 rmistry@google.com Download material design SVGs from Google Storage
2017-07-19 brianosman@google.com Some basic Flutter/Fuchsia docs
2017-07-19 jshin@chromium.org Add aliases mapping Windows CJ fonts to Noto Serif CJK
2017-07-19 bsalomon@google.com Revert "Revert "Make GrAtlasTextOp a non-legacy GrMeshDrawOp""
Test: Presubmit checks will test this change.
Change-Id: I2d60862680614274627158fcb39e0efe38acdd5b