Roll Skia and remove PngPixelSerializer

[brianosman]

SkPixelSerializer has been removed, and the default behavior for SkPicture serialization is the same as what was being done here before.

[brianosman]

Hmm - I didn't modify the file that's failing the format check. How did that land originally?

[jason-simmons]

The format warning was introduced by #4471

Looks like that PR didn't pass the Travis check:
https://travis-ci.org/flutter/engine/builds/318042055?utm_source=github_status&utm_medium=notification

[Hixie]

When this rolled into Flutter in flutter/flutter#13696, there was a more than 2x regression on flutter_gallery__transition_perf worst_frame_rasterizer_time_millis. This is not the only commit that was involved, but it's the most suspicious.

[brianosman]

Here's the list of Skia commits included in that roll: https://skia.googlesource.com/skia.git/+log/58a3fcd4..ef038483

Eyeballing the list - ~140 commits? Is it easy to reproduce this, to perform some kind of bisect (into the roll)?