Unofficial gardening. Mark some fast/canvas tests as flakily crashing.

BUG=269100
TBR=fmalita

Review URL: https://codereview.chromium.org/22605005

git-svn-id: svn://svn.chromium.org/blink/trunk@155707 bbb929c8-8fbe-4397-9dbb-9b2b20218538