DevTools: extract TimelineModel.Record from TimelinePresentationModel.Record.

This change splits the model and presentation parts of the timeline recod. Now model + all views operates modal records. TimelineView wraps them in presentation records. Next step is to move filters out of presentation model and make it private to the TimelineView.

R=caseq@chromium.org

Review URL: https://codereview.chromium.org/183893010

git-svn-id: svn://svn.chromium.org/blink/trunk@168290 bbb929c8-8fbe-4397-9dbb-9b2b20218538