Mark various compositing tests as flaky on Mac
Mark various compositing tests as flaky on Mac

Unreviewed gardening.

BUG=310679
TBR=pfeldman@chromium.org,ccameron@chromium.org

Review URL: https://codereview.chromium.org/37503003

git-svn-id: bf5cd6ccde378db821296732a091cfbcf5285fbd@160350 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs