Timeline: use Array.mergeOrdered() to merge records

R=alph@chromium.org, alph, vsevik
BUG=

Review URL: https://codereview.chromium.org/169593002

git-svn-id: svn://svn.chromium.org/blink/trunk@167306 bbb929c8-8fbe-4397-9dbb-9b2b20218538