Add suppressions for flaky compositing/layer-creation tests.

TBR=vollick@chromium.org
BUG=321358

Review URL: https://codereview.chromium.org/76893002

git-svn-id: svn://svn.chromium.org/blink/trunk@162319 bbb929c8-8fbe-4397-9dbb-9b2b20218538