Roll external/skia 26acbe8a8..e94871bf8 (1 commits)

https://skia.googlesource.com/skia.git/+log/26acbe8a8..e94871bf8

2017-08-28 angle-deps-roller@chromium.org Roll skia/third_party/externals/angle2/ 97577623f..7e1197e01 (1 commit)

Test: Presubmit checks will test this change.
Change-Id: I45683cbd07c7a7821ac9648188368328355ba282