Implement SkFontMgr_Custom::onCreateFromFontData.

This fixes serialization issues. We could create a non-default gx
typeface, but not deserialize it correctly.

GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2057293002

Review-Url: https://codereview.chromium.org/2057293002
1 file changed