Roll external/skia c857956fa..f2889f1c5 (12 commits)

https://skia.googlesource.com/skia.git/+log/c857956fa..f2889f1c5

2018-08-08 djsollen@google.com Revert "Update ShouldUseAAA with our better complexity estimation"
2018-08-08 robertphillips@google.com First version of incremental topological sort
2018-08-08 angle-skia-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com Roll third_party/externals/angle2 b983a4b28b83..c93eeaab1526 (1 commits)
2018-08-08 recipe-roller@chromium.org Roll recipe dependencies (trivial).
2018-08-08 recipe-roller@chromium.org Roll recipe dependencies (trivial).
2018-08-08 caryclark@skia.org add json dump to pathops unittest
2018-08-08 mtklein@google.com make sksg a component
2018-08-08 reed@google.com use VectorValue consistently
2018-08-08 recipe-roller@chromium.org Roll recipe dependencies (trivial).
2018-08-08 herb@google.com Remove unused TextPathIter
2018-08-08 liyuqian@google.com Update ShouldUseAAA with our better complexity estimation
2018-08-08 angle-skia-autoroll@skia-buildbots.google.com.iam.gserviceaccount.com Roll third_party/externals/angle2 1bd4bfb0c2d8..b983a4b28b83 (2 commits)

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Change-Id: I8080611eecfe30c8df80f3619d98cebba5674f62
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