Timeline: bring back FirstPaint marker and remove brown ticks near frame markers

- implement synthetic FirstPaint markers on front-end (they used to be generated
    on the back-end with old Timeline instrumentation which is an ex-parrot)
- remove brown marks near the frame markers (regressed at r177959)

BUG=

Review URL: https://codereview.chromium.org/732683002

git-svn-id: svn://svn.chromium.org/blink/trunk@185392 bbb929c8-8fbe-4397-9dbb-9b2b20218538