Add tracing/timeline-timer.html as flaky.
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: bf5cd6ccde378db821296732a091cfbcf5285fbd@180955 bbb929c8-8fbe-4397-9dbb-9b2b20218538

primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs,primiano/blink-gitcs