Add test for platform encoders, turn off platform encoders by default

Clients that like WIC and CG can still use them.  And we can be
confident about that, since we now test WIC and CG.

Let Skia always use our own encoders by default, so we can do cool,
custom things on all platforms.

BUG=skia:
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2250683003

Review-Url: https://codereview.chromium.org/2250683003

0 files changed, 0 insertions, 0 deletions