Webkit: use fabs() for double

fabsf() is for float, use fabs() for double instead.

BUG=chromium:348044

Review URL: https://codereview.chromium.org/176713008

git-svn-id: svn://svn.chromium.org/blink/trunk@168557 bbb929c8-8fbe-4397-9dbb-9b2b20218538