Roll external/skia 0a57971f0..fbc887df7 (1 commits)

https://skia.googlesource.com/skia.git/+log/0a57971f0..fbc887df7

2019-03-05 reed@google.com Revert "Remove (unnecessary?) flush in RenderYUVAToRGBA"

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Change-Id: I2943e00799adcf367b12f50e482b84083119dff3
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