Roll external/skia 790395724..9435ee3cf (5 commits)

https://skia.googlesource.com/skia.git/+log/790395724..9435ee3cf

2018-09-24 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/angle2 f668a4b5fb72..5272a543705e (1 commits)
2018-09-24 jvanverth@google.com More valid input checking for text
2018-09-24 bsalomon@google.com Revert "[skottie] Initial property setters"
2018-09-24 bungeman@google.com Filter TextBlob paints in Viewer.
2018-09-24 michaelludwig@google.com Revert "Implement an explicit binary search-based analytic gradient colorizer"

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: I4d2bbe6af146f2581f7f6e3c5a27f210961ec9cf
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.