GitLab

optipng sometimes finds that using indexed color yields a smaller PNG
file. Allow that.

Also add a comment to the sRGB code explaining why that value was
chosen.

Bug: 846451
Change-Id: Ia8d6ef7dba59e4a0a0cbbf4d3122f63c501cfabf
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/2148030
Commit-Queue: Avi Drissman <avi@chromium.org>
Reviewed-by: Mark Mentovai <mark@chromium.org>
Cr-Commit-Position: refs/heads/master@{#759421}