Roll external/skia 45a6f147b..f57c6de78 (4 commits)

https://skia.googlesource.com/skia.git/+log/45a6f147b..f57c6de78

2017-09-29 jvanverth@google.com Revert "Enable coverage counting path rendering on non-Android"
2017-09-29 reed@google.com Just add new safe size apis
2017-09-29 csmartdalton@google.com Enable coverage counting path rendering on non-Android
2017-09-29 liyuqian@google.com Add a new calmbench tool for noiseless nanobench

Test: Presubmit checks will test this change.
Change-Id: I2b84190b2b14210bc80ae9d200b4f8bc0f791091
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