DevTools: Tune JS frames colors on Timeline Flamechart.

Get rid of colors zoo. Make use just two colors for odd and even lines instead.

BUG=363976

Review URL: https://codereview.chromium.org/589483002

git-svn-id: svn://svn.chromium.org/blink/trunk@182487 bbb929c8-8fbe-4397-9dbb-9b2b20218538