DevTools: move JS sampling Timeline out of experimental

Added "Sampling" option on Timeline. When it is enabled we will stack JavaScript sampling profiler when Timeline is recorded and then will merge JS samples into Timeline events on the flame chart view.

BUG=363976

Review URL: https://codereview.chromium.org/661023002

git-svn-id: svn://svn.chromium.org/blink/trunk@183864 bbb929c8-8fbe-4397-9dbb-9b2b20218538