Have DM manually encode its .png outputs.

This eliminates some variability on various axes: different PNG encoders, different libpng versions, different formats (RGB, indexed), different unpremultiplication, different sRGB tags.

BUG=skia:

Committed: https://skia.googlesource.com/skia/+/3cc0dfffb70c0bd08ed8899efcd2e98da86a6ec7

CQ_EXTRA_TRYBOTS=client.skia:Test-Win8-MSVC-ShuttleB-CPU-AVX2-x86_64-Debug-Trybot

Review URL: https://codereview.chromium.org/1304443002
3 files changed