Add tracing/timeline-timer.html as flaky.

BUG=407915
TBR=tkent@chromium.org
NOTRY=true

Review URL: https://codereview.chromium.org/513733002

git-svn-id: svn://svn.chromium.org/blink/trunk@180955 bbb929c8-8fbe-4397-9dbb-9b2b20218538