TestExpecations: inspector-protocol/layers/get-layers.html LayoutTests flaky

BUG=280658
TBR=rjkroege@chromium.org

Review URL: https://codereview.chromium.org/23651005

git-svn-id: svn://svn.chromium.org/blink/trunk@156872 bbb929c8-8fbe-4397-9dbb-9b2b20218538