The script for the time line plot has been broken since r15484, which
changed the format of tick entries in v8.log.

To prevent this from happening in the future, I added a test case.

R=hpayer@chromium.org
BUG=

Review URL: https://codereview.chromium.org/18826008

git-svn-id: http://v8.googlecode.com/svn/branches/bleeding_edge@15581 ce2b1a6d-e550-0410-aec6-3dcde31c8c00