Roll external/skia 915893167..f3b9d4b03 (2 commits)

https://skia.googlesource.com/skia.git/+log/915893167..f3b9d4b03

2017-06-22 halcanary@google.com SkPDF: add some TRACE_EVENTs
2017-06-22 mtklein@chromium.org fix repeat/mirror sampling bleed

Test: Presubmit checks will test this change.
Change-Id: I8064d4536ad1d0754a226bb144382c1db54ac690