Mark fast/dom/timer-throttling-hidden-page.html as flaky on debug and ASAN

TBR=dglazkov@chromium.org

Review URL: https://codereview.chromium.org/136393007

git-svn-id: svn://svn.chromium.org/blink/trunk@166203 bbb929c8-8fbe-4397-9dbb-9b2b20218538