Mark inspector/timeline/timeline-window-filter.html as flaky.

BUG=339252
TBR=loislo

Review URL: https://codereview.chromium.org/147983010

git-svn-id: svn://svn.chromium.org/blink/trunk@166055 bbb929c8-8fbe-4397-9dbb-9b2b20218538