Roll external/skia bba465b98..d2a590893 (1 commits)

https://skia.googlesource.com/skia.git/+log/bba465b98..d2a590893

2018-12-07 skia-autoroll@skia-public.iam.gserviceaccount.com Roll third_party/externals/angle2 ec06305b8216..7c985f5c4f1a (2 commits)

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https://skia.googlesource.com/buildbot/+/master/autoroll/README.md

If the roll is causing failures, please contact the current sheriff, who should
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Test: Presubmit checks will test this change.
Change-Id: I902d5d2ce5bef68861696cbe3923218322abf87d
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.