Mark virtual/deferred/inspector/timeline/tracing/decode-resize.html as flaky on Mac

TBR=ager@chromium.org

Review URL: https://codereview.chromium.org/316543002

git-svn-id: svn://svn.chromium.org/blink/trunk@175351 bbb929c8-8fbe-4397-9dbb-9b2b20218538