Roll external/skia 08b79b73a..ddfd2a662 (2 commits)

https://skia.googlesource.com/skia.git/+log/08b79b73a..ddfd2a662

2017-08-14 robertphillips@google.com Use kLow_SkFilterQuality in generateGlyphImage
2017-08-14 mtklein@chromium.org we never define BLEND_MODE

Test: Presubmit checks will test this change.
Change-Id: Id81ffcc70f9ddbeeae60c7ff41a5dde26dc56d10