Roll external/skia d4c7458f6..275eaff3b (5 commits)

https://skia.googlesource.com/skia.git/+log/d4c7458f6..275eaff3b

2019-01-04 kjlubick@google.com [pathkit] Add .ready() to initialize
2019-01-04 ethannicholas@google.com Fixed GL shader link status checks
2019-01-04 kjlubick@google.com [canvaskit] Add .ready() which is a real promise
2019-01-04 reed@google.com change paint serialization to exclude font-related fields
2019-01-04 herb@google.com Update SkDescriptor

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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
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Test: Presubmit checks will test this change.
Change-Id: Iac8c16a511e36ee370376caf9e70b53d124cd3c3
Exempt-From-Owner-Approval: The autoroll bot does not require owner approval.