Update image testing to version 6

This replaces the old HTC.dng test image (~40 MB) with a much smaller
HTC.dng (~125 kb).

This should limit OOM errors on our bots and improve the speed of the
tests suite.

BUG=skia:5283
BUG=skia:5307
GOLD_TRYBOT_URL= https://gold.skia.org/search?issue=2004113002

Review-Url: https://codereview.chromium.org/2004113002
1 file changed