Roll external/skia c25f440d5..11f4994b8 (19 commits)

https://skia.googlesource.com/skia.git/+log/c25f440d5..11f4994b8

2018-09-21 brianosman@google.com Revert "Reland "Preserve colorType and alphaType in SkImage::makeColorSpace""
2018-09-21 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/swiftshader 9f6c0b899ae6..c5e68abdea9e (1 commits)
2018-09-21 brianosman@google.com Cleanup SkPatchUtils, stop using SkColorSpaceXform
2018-09-21 mtklein@google.com focus exported color apis
2018-09-21 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/angle2 ab5fb5edb186..9d84ccbaf233 (1 commits)
2018-09-21 caryclark@skia.org move color4f docs to in progress
2018-09-21 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/swiftshader 4daedcd8c612..9f6c0b899ae6 (2 commits)
2018-09-21 brianosman@google.com Introduce SkRGBA4f, templated on SkAlphaType
2018-09-21 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/swiftshader c89f75b65555..4daedcd8c612 (1 commits)
2018-09-21 halcanary@google.com Docs: update to docs from a4daf19319
2018-09-21 halcanary@google.com SK_SUPPORT_LEGACY_DOCUMENT_FACTORY: clean up part 1/2
2018-09-21 herb@google.com Regularize path cache lookup with Mask and Fallback
2018-09-21 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/swiftshader 2ecc8b712b08..c89f75b65555 (1 commits)
2018-09-21 jvanverth@google.com Optimize SkTriangulateSimplePolygon.
2018-09-21 robertphillips@google.com Fix Chrome iOS builder
2018-09-21 caryclark@skia.org sync color4f with docs
2018-09-21 lsalzman@mozilla.com mark SkCanvas layer device as immutable before compositing it on restore
2018-09-21 brianosman@google.com Reland "Preserve colorType and alphaType in SkImage::makeColorSpace"
2018-09-21 caryclark@skia.org doc change for getAlphaf

The AutoRoll server is located here: https://autoroll-internal.skia.org/r/android-master-autoroll

Documentation for the AutoRoller is here:
https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
be CC'd on the roll, and stop the roller if necessary.

Test: Presubmit checks will test this change.
Change-Id: Icc18ebbc1bc3ce96d624917051ab4aa069defb51
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.