The gm output on different font platforms is so different
that comparing images in Gold has little value. Separate the
images by appending platform information to the gm name to
group somewhat similar images together.
Note that this does not attempt to make sure that all images
generated by Gold are nearly pixel identical; it only reduces
the number of nonsensical comparisons.
R=bungeman@google.com
Review URL: https://codereview.chromium.org/1245643002
