Roll external/skia e94871bf8..2e86634ae (5 commits)

https://skia.googlesource.com/skia.git/+log/e94871bf8..2e86634ae

2017-08-28 bsalomon@google.com Move transformation of clip elements to SkClipStack::Element
2017-08-28 csmartdalton@google.com Add a GrCCPRGeometry file
2017-08-28 angle-deps-roller@chromium.org Roll skia/third_party/externals/angle2/ 7e1197e01..3ef140a97 (2 commits)
2017-08-28 reed@google.com add 'a8' config for nanobench, specialize blitV for raster-pipeline
2017-08-28 halcanary@skia.org SkPDF: SkWStream::write -> SkWStream::writeText

Test: Presubmit checks will test this change.
Change-Id: Id7b665e549bf34f5d9ab410a946e7feec18634ed