Compress PNGs with zopflipng

Compress PNGs with zopflipng

Zopfli is the most efficient DEFLATE compression algorithm, trading run-time
performance for file sizes that are typically 3-8% smaller than those produced
by zlib with the maximum compression setting. Its output is Deflate-compatible,
so no specialized decoder is needed.

This change was created by running zopflipng against all the PNG files in this
repository. The exact invocation was:

  git ls-files --exclude-per-directory=.gitignore -- '*.png' \|
    parallel zopflipng -m -y {} {} \;

Files which zopflipng was not able to compress more efficiently were left unmodified.

Bug: T127608
Change-Id: Ia9c70cf35da489985af39df1f8b58469eb4813fd