Mark fast/dom/timer-throttling-background-page-near-alignment-interval.html as Slow.

[Insert ironic meme here.]

BUG=24182
TBR=

Review URL: https://codereview.chromium.org/109943005

git-svn-id: svn://svn.chromium.org/blink/trunk@164276 bbb929c8-8fbe-4397-9dbb-9b2b20218538