[SP] Document sub-pixel-transparency-layer.html failure
[SP] Document sub-pixel-transparency-layer.html failure

Ref test failure triggered by missing --enable-slimming-paint reference arg.

BUG=472817
TBR=pdr@chromium.org,chrishtr@chromium.org,wkorman@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/1053123005

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@193916 bbb929c8-8fbe-4397-9dbb-9b2b20218538

XiaosongWei/blink-crosswalk,smishenk/blink-crosswalk,PeterWangIntel/blink-crosswalk,Bysmyyr/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,XiaosongWei/blink-crosswalk,Bysmyyr/blink-crosswalk,Bysmyyr/blink-crosswalk,PeterWangIntel/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,XiaosongWei/blink-crosswalk,XiaosongWei/blink-crosswalk,XiaosongWei/blink-crosswalk,PeterWangIntel/blink-crosswalk,Pluto-tv/blink-crosswalk,Pluto-tv/blink-crosswalk,Bysmyyr/blink-crosswalk,PeterWangIntel/blink-crosswalk,XiaosongWei/blink-crosswalk,smishenk/blink-crosswalk,Bysmyyr/blink-crosswalk,XiaosongWei/blink-crosswalk,PeterWangIntel/blink-crosswalk,PeterWangIntel/blink-crosswalk,smishenk/blink-crosswalk,Bysmyyr/blink-crosswalk,PeterWangIntel/blink-crosswalk,XiaosongWei/blink-crosswalk,Bysmyyr/blink-crosswalk,Bysmyyr/blink-crosswalk,smishenk/blink-crosswalk,Pluto-tv/blink-crosswalk,PeterWangIntel/blink-crosswalk,smishenk/blink-crosswalk,Pluto-tv/blink-crosswalk,PeterWangIntel/blink-crosswalk,smishenk/blink-crosswalk,smishenk/blink-crosswalk,smishenk/blink-crosswalk,smishenk/blink-crosswalk,smishenk/blink-crosswalk,Pluto-tv/blink-crosswalk,Bysmyyr/blink-crosswalk,XiaosongWei/blink-crosswalk,PeterWangIntel/blink-crosswalk,Bysmyyr/blink-crosswalk,XiaosongWei/blink-crosswalk,Pluto-tv/blink-crosswalk