DevTools: convert memory into the timeline recording mode (as opposed to presentation). Frames is now a pure presentation mode.

R=caseq@chromium.org

Review URL: https://codereview.chromium.org/242423003

git-svn-id: svn://svn.chromium.org/blink/trunk@172028 bbb929c8-8fbe-4397-9dbb-9b2b20218538