Partial revert of r178392

An unnecessary modification that was made in Blink r178392 was causing
a regression in the rendering of the inspector timeline.  Pulling it out

BUG=408080
R=kbr@chromium.org

Review URL: https://codereview.chromium.org/541783002

git-svn-id: svn://svn.chromium.org/blink/trunk@181400 bbb929c8-8fbe-4397-9dbb-9b2b20218538